Process Check Valves

NOTE This standard covers the check valve furnished as an individually specified product on a pump discharge or a process line in a water, wastewater, or industrial plant and its pump stations: the valve that lets the pump fill the line and holds the line's contents off the pump when the pump stops. (1.1)

NOTE The boundary of the work is the valve as a shop-assembled unit: the body and its end connections, the closure member and its seat, the hinge, shaft, or guide that carries the closure member, the lever, weight, spring, dashpot, or cushion that governs how it closes, the position indicator and limit switches where furnished, the shop coating, and the shop tests, together with the installation, the adjustment on the running pump, and the field closure test that prove it in the line. (1.2)

NOTE A check valve is the one valve in a pump station that operates itself, on every start and every stop, for the life of the station, and the one that destroys the station when it operates wrong. A disc that is still open when the column reverses is slammed shut by the reversing flow, and the pressure rise that follows the slam travels back down the main as a water hammer that lifts pumps off their bases and splits pipe. The type, the closure assist, and the cushioning of a pump discharge check valve are chosen against the deceleration of the column it holds, which is a property of the piping system and of the pump, and that is why this standard carries the closure response as a selection per valve and is prescriptive about adjustment on the running pump. (1.3)

NOTE AWWA C508 describes the swing check valve of waterworks service, 2 in. through 48 in., with a full waterway and an externally mounted lever, and AWWA C518 the dual-disc valve that closes under spring load between two flanges. MSS SP-125 describes the spring-loaded center-guided silent check of iron bodies, and API 594 the wafer, lug, and flanged check valves of industrial piping. The tilting-disc, ball, rubber flapper, foot, and duckbill valves have no consensus product standard of their own and are furnished to the manufacturer's published design, tested at the pressures of AWWA C508 or API 598 as this standard directs for each. (1.4)

NOTE This standard is read with Common Work Results ProcessCommon Work Results for Process EquipmentResolves to the current adopted revision.sync/common-work-results-process, which carries the submittal register, the factory and witnessed test policy, the manufacturer's field services, the data nameplate, the anchorage basis, and the warranty and spare parts administration for every process valve, and nothing here restates them. (1.5)

NOTE A check valve is a product of the piping it sits in and of the pump it protects, and the standards that govern each stay where they are. The pump discharge check valve on a horizontal, vertical turbine, submersible, or positive displacement process pump is furnished under this standard; the isolation valve beside it, the air valve ahead of it, and the actuator on that isolation valve are furnished under their own standards. (1.8)

NOTE The following are outside this scope and are governed by the standards named. (1.9)

NOTE Pump control valves, surge anticipator valves, surge relief valves, and the other pilot-operated automatic control valves of a pump station, and thermoplastic ball, diaphragm, and check valves for chemical feed service, are not yet owned by a SynC standard. (1.10)

NOTE A check valve on a buried site water main or on a sewage force main outside the station is furnished under the standard governing that main, which specifies it with the main, unless the valve schedule designates it as furnished under this standard. (1.11)

NOTE The closure data is the submittal that catches the error on this product. A swing check that is right in every material and rating still slams on a short, steep force main, and the manufacturer that has the deceleration in hand is the only party able to say before shipment whether its lever and weight, its spring, or its dashpot will close the disc in time. (3.1.3)

NOTE A valve shipped bare and fitted with a lever and weight in the field arrives with nobody responsible for the weight position, and the weight position is the one adjustment that decides whether the valve slams. The valve manufacturer is the party that knows its own disc mass and seat angle, so the initial setting is made where that is known and refined on the running pump. (4.2.3)

NOTE Each check valve on the project is either a pump discharge valve, installed between a pump and its isolation valve, or a process line valve, installed in a line to keep it from draining back or from being fed from the wrong direction, and the valve schedule names which each is. (5.1.2)

NOTE Size and rating are properties of each location on a project, and a standard that asserts either has decided the hydraulics. The valve schedule carries them per tag, and this standard carries what every valve of a given type has in common. (5.1.3)

NOTE The closure response is the Engineer of Record's answer to a hydraulic question this standard does not ask: how fast the column in the discharge piping decelerates when the pump stops, which depends on the static head, the length and profile of the main, the pump's inertia, and whether the stop is a normal one or a power failure. On a low-head, long, flat main the column coasts for seconds and an unassisted disc drops closed before anything reverses. On a high-head or short, steep main the column reverses in a fraction of a second, and the disc has to be already closing as the forward flow decays, by a weight or a spring, or already closed, by a spring strong enough to shut it before the reversal, or closed softly against the reverse flow by a cushion that takes the last part of the travel slowly. Where the surge analysis finds that a fast closure itself produces an unacceptable pressure rise, the last response, a timed closure that lets a controlled reverse flow pass while the disc completes its travel, is what the analysis asks for, and only a dashpot-controlled swing or tilting-disc valve delivers it. The response differs per pump group on most plants, which is why it is read from the valve schedule rather than defaulted. (5.2.3)

NOTE Valves in exposed service are those installed in a building, a gallery, a vault, or above grade, where the cover, the lever, and the switches are reachable by hand; valves in buried service are those installed in a trench and backfilled. A check valve has no operator, so a buried check valve has no valve box and no extension stem, and whatever is bolted to its outside is out of reach until the valve is dug up. (5.3.1)

NOTE A dashpot filled with an oil chosen for a heated gallery thickens in a January vault and closes the valve a second late, which is the slam the dashpot was bought to prevent. A vault below the water table floods, and a limit switch sealed for rain fills with water on the first flood and reports the valve closed from then on. The temperature range and the groundwater elevation are project facts, and the ratings follow them. (5.3.5)

NOTE A swing check gives the full waterway and the lowest head loss of the metal-disc valves, is serviced through its cover without removing it from the line, and carries the lever that lets the closure be assisted, cushioned, indicated, and switched; its disc has the longest travel of the group and is the one that slams where the column reverses quickly. A tilting-disc valve pivots its disc on trunnions just above center so the disc travels a short arc and closes in a fraction of a swing check's time, at a higher head loss and at a price several times the swing check's, and it is the valve of high-head, large pumps where a swing check cannot be made to close in time. A silent check closes its spring-loaded disc as the forward flow decays and is shut before the column reverses, with no lever, no indication, and no cushioning, at the highest head loss of the group, and it is the valve of booster stations and of plant water lines where the pressure rise of a fast closure is tolerable and the outside of the valve is nobody's concern. A nozzle check is a silent check built around a venturi body, so its disc is short-travel and its head loss is the lowest of the spring-closed valves, at a price above the tilting disc, and it is selected on large high-service pumps where both the slam and the head loss matter. A dual-disc wafer valve closes two spring-loaded half discs between two flanges in the shortest laying length and at the lowest weight and cost, serves a process line well, and is sized for a pump discharge only where the surge analysis has accepted its closure. A rubber flapper valve closes a steel-reinforced elastomer disc on a flex hinge through a short travel at a 45° seat, with no metal hinge pin to wear and the lowest cost of a serviceable body, and it is limited in pressure and in the sizes made. No type is the norm across the water services this standard covers, so none is defaulted. (6.1.2)

NOTE A swing check with a full waterway passes the solids the pump passes, holds its disc clear of the flow when open, carries the lever and weight that the raw sewage pump discharge is almost always furnished with, and shows the plant from across the gallery whether the pump is moving water, which is why it is the valve on nearly every wastewater pump discharge and the default here. A rubber flapper valve seals on a rag or a stone that would hold a metal disc off its seat, is the quietest of the group, and is chosen on smaller stations and on scum lines where the fluid is the problem rather than the surge. A ball check has no hinge or seat to foul, clears itself of solids on every cycle, is the valve of grinder and small sewage pumps, and does not indicate its position or accept a lever or a switch. A tilting disc is selected on large raw sewage pumps on high-head force mains where the swing check cannot be made to close in time, at the cost of a seat that solids reach. (6.2.2)

NOTE A ball check is the valve of thick sludge and grit, because the ball rolls off its seat on every stroke and nothing in the body offers a ledge for solids to pack onto, and because a positive displacement pump's pulsing flow lifts and reseats a ball cleanly where it hammers a hinged disc on every stroke. A swing check serves thin sludge and the discharge of a rotary lobe or progressing cavity pump whose flow is nearly steady, with the lever and weight to damp the pulsation, and it needs its cover opened wherever grit packs under the disc. A rubber flapper valve seals on grit and on the stringy solids of a scum line and is chosen where the pressure and the size are within its range. A positive displacement pump cannot run against a closed discharge without its relief, and some plants omit the check valve on a sludge pump whose discharge is isolated by a plug valve and protected by a relief, because the check is the one component in the line that fouls; where the line can drain back through the pump or a second pump discharges into the same header, the check valve is not optional. No type is the norm across these services, so none is defaulted. (6.3.2)

NOTE The rating that matters for a check valve is the reverse one. The valve is open under forward pressure and has nothing to hold; it is closed, with the static head of the main and the surge on its downstream face and an open pump on the other, when it is working, and that is the condition the seat test applies. AWWA C508 rates its swing checks by size at the working pressure the standard states, and manufacturers offer heavier bodies above it for high-head discharges, which is why the rating is read from the valve schedule rather than fixed here. (7.1.4)

NOTE Class 125 drilling matches the flanges of every ductile iron fitting and flanged pipe in a plant and every iron valve beside it, and it is what the valve is bolted to on nearly every project. Class 250 drilling is selected where the connected piping is Class 250 or Class 300 for a pressure above the Class 125 rating, and the heavier flange needs the heavier body behind it. (7.2.4)

NOTE Flanged ends are the connection of exposed plant piping, where the valve is bolted between flanges it is unbolted from for service, and they are offered on every type and in every size. Mechanical joint ends take the gasket and gland of a buried ductile iron main and are the ends of a direct-buried swing or flapper valve. Grooved ends suit a grooved process piping system in the sizes the coupling manufacturer rates for the line pressure. A wafer body is clamped between two flanges by through-bolts, is the body of the dual-disc and most silent checks, and cannot hold pressure with either flange unbolted; a lug body bolts to each flange by tapped lugs and serves a dead end the wafer body cannot. Threaded ends are offered on small swing, silent, and ball checks and suit a threaded sludge, drain, or seal water line. The connection follows the piping at each location rather than the valve, which is why it is read from the valve schedule. (7.3.2)

NOTE Requirements in this section apply to every swing check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (8.1.1)

NOTE AWWA C508 is the standard every water and wastewater utility buys its swing checks against, and it requires the full waterway, the external lever, and the shell and seat tests the rest of this section relies on. MSS SP-71 and MSS SP-136 describe the gray and ductile iron swing checks of industrial piping, which are shorter, available threaded in the small sizes, and rated by cold-working pressure rather than by the AWWA size rating, and they serve the plant's industrial and seal water lines where the AWWA valve is longer than the piping has room for. (8.1.4)

NOTE Ductile iron carries the same pressure rating as gray iron at a lighter section and survives the bolting stress and the impact that crack a gray iron body, and it is the body of the heavier-rated valves and of nearly every valve made for buried or force main service. Gray iron is the body AWWA C508 was written around, is the lower-cost casting, and remains the body many utilities stock and specify for the plant gallery where nothing strikes it. A stainless steel body is selected where the fluid attacks coated iron, as in seawater, brine, or a chemical solution, and it removes the coating as a maintenance item at several times the cost. A bronze body is offered in the small sizes only and is the body of a threaded seal water or sample line valve. Neither iron is the norm across manufacturers and sizes, so no body is defaulted. (8.2.2)

NOTE A disc that cannot turn on its arm seats on the same line every time, and the groove it wears there is the leak the valve develops in its fifth year. A seat ring that is part of the casting is replaced by replacing the valve. (8.2.7)

NOTE A resilient seat seals drop-tight on a disc that has landed slightly off its line and on a particle a metal seat would hold open, which is why it is the seat of nearly every swing check in water and wastewater service and the default here; it is the one part of the valve that wears, and it is replaced from the cover. A metal-to-metal seat has nothing to replace and tolerates a temperature and a fluid no elastomer serves, at the cost of a seal that weeps on any imperfection, and it is selected on hot or chemical industrial lines and by utilities that have standardized on it. Among the elastomers, nitrile resists oils, grease, and hydrocarbons and swells in chloraminated water over years, which makes it the usual seat in wastewater, sludge, and raw water and a poor one downstream of chloramination. EPDM resists chlorine, chloramine, and ozone and is attacked by petroleum oils, which makes it the usual seat in treated and potable water and a poor one in raw sewage. Neoprene sits between the two on oil resistance and is specified where a utility's stock is neoprene. Natural rubber has the greatest abrasion resistance of the group and is selected for grit-laden water at the cost of ozone and oil resistance. Fluoroelastomer resists chemicals that attack all four and is selected for chemical and hot industrial service at several times the cost. No compound is the norm across the services this standard covers, so none is defaulted. (8.3.3)

NOTE The hinge pin is the one part of a swing check that moves on every cycle and sits wetted between cycles, and the one that seizes where it corrodes. Type 304 serves treated water where chlorides are low and is the AWWA C508 baseline. Type 316 resists chloride pitting in wastewater, in chloraminated water, and in a vault that floods, at a small premium, and is what most wastewater specifications call for. A nickel-copper alloy resists seawater and brine where both stainless grades pit. No grade is the norm across the services this standard covers. (8.4.2)

NOTE A free-swinging disc closes under its own weight and the reversing flow, has nothing outside the body to seal, adjust, or be struck, and is the swing check of a process line and of a low-head pump on a long main, where the column reverses slowly. A lever and weight starts the disc closing as the forward flow decays, so the disc is near its seat when the column reverses, shows the disc position to anyone in the gallery, gives the limit switch something to trip, and is the provision on nearly every wastewater and raw water pump discharge; the weight's position on the lever is the adjustment that tunes the closure to the pump, and a weight set too far out holds the disc partly closed against the running pump and costs head. A lever and spring does the same work in less room, closes faster than a weight on the same disc because the spring force does not fall off as the disc rises, and is the provision on short, high-head mains where a weight cannot close the disc in time; its closing force is not visible the way a weight's is, and it is adjusted with a tool. The provision follows the closure response of each pump discharge, which is why none is defaulted across a project. (8.5.2)

NOTE Most swing checks need no cushioning, because the lever and weight or spring closes the disc before the reversal or the reversal is slow enough that a free disc lands softly, and that is why none is the default. Where the surge analysis finds that the disc is still open when the column reverses and that the slam is unacceptable, a cushion takes the last part of the travel slowly. An air cushion is a piston in a vented cylinder on the lever that resists the closing travel through a bleed orifice; it is the simplest and cheapest cushion, holds no fluid to leak, and its setting drifts with temperature and with the wear of the piston. An oil dashpot is the same piston in a sealed oil-filled cylinder with an adjustable orifice; it holds its setting across years and temperatures, lets the closing time be set on the running pump, and is the cushion of the large high-head pump discharge, at a cost that includes the oil and its seals. A bottom-mounted buffer is a piston in the body below the disc that the disc strikes over the last few degrees of its travel, cushioning the seat contact without touching the lever; it is fitted where the lever is spring-loaded for a fast close and the seat impact itself is the problem, and where the lever cannot carry a cylinder in the space available. Each cushion lets the valve close most of its travel freely and controls only the end, so a cushioned valve is still a closing valve and not a slow one. (8.6.2)

NOTE A backflow actuator is a screw or a lever on the cover or the hinge shaft that holds the disc off its seat by hand, so that the force main drains back through the pump to the wet well to flush the pump or to drain the main for work on it, and it is bought on a sewage pump station whose plant has no other way to drain the main. Most plants drain a main through a drain valve or a cleanout and need no actuator, which is why it is not furnished by default; a plant that uses one takes on the risk that the disc is left held open and the station floods on the next stop. (8.7.2)

NOTE Requirements in this section apply to every resilient-hinge rubber flapper check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (9.1)

NOTE The flapper is both the seal and the hinge, so its compound is chosen for the flex life in the fluid as much as for the seal. Nitrile is the compound nearly every flapper valve is molded in, resists the grease and oil of raw sewage, and is the default; EPDM is selected on chlorinated and chloraminated water where nitrile swells over years, neoprene where a utility's stock is neoprene, and fluoroelastomer on a chemical line, at several times the cost and with a shorter flex life. (9.5)

NOTE The flapper valve's advantage over a swing check is the absence of a hinge pin, which is the swing check's wearing part and the one that seizes, and its 45° seat and short travel are what let it close before the column reverses on most mains without a lever or a weight. Its limit is the reinforced rubber disc, which carries the reverse pressure as a plate and sets the pressure and the size the valve is made in, and a plant that needs a flapper valve above that range needs a different type. (9.10)

NOTE Requirements in this section apply to every tilting-disc check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (10.1)

NOTE A tilting disc without a dashpot closes faster than any swing check, which is why it is bought, and the speed of that closure is itself the pressure rise where the main is long and the head is high. A top-mounted dashpot slows both the opening and the closing through an oil cylinder on a shaft extended from the trunnion; it damps the disc flutter of a pump that runs at the edge of its curve and controls the closure where the whole travel has to be timed. A bottom-mounted dashpot acts only over the last part of the closing travel, through a piston the disc strikes, and it is the arrangement where a fast free closure is wanted and only the seat impact is to be cushioned. Both are fitted where the surge analysis calls for a two-stage closure, fast through the first part and timed through the last. The provision follows the surge analysis of each pump discharge, which is why none is defaulted. (10.7)

NOTE Requirements in this section apply to every silent spring-loaded center-guided check valve and every nozzle check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (11.1)

NOTE A wafer silent check is the shortest and lightest check valve made, costs the least, and is clamped between two flanges it cannot be removed from without unbolting the line; its disc travel is short and its head loss is the highest of the three. A globe-style flanged body carries the same spring-loaded disc in a body that bolts to the line independently and holds pressure with either flange removed, at a laying length that fits where a swing check fits. A flanged nozzle body shapes the flow through a venturi so that the disc or ring travels a few inches on a straight diffuser, at the lowest head loss of any spring-closed valve and the fastest closure of any check valve, and it is the body of the large high-service pump discharge where both the slam and the energy cost of head loss have been computed. (11.5)

NOTE A silent check closes under spring force rather than under reverse pressure, so a resilient seat gives it the drop-tight seal a metal seat on a spring cannot, at the cost of the one wearing part, and a metal seat is chosen where the fluid is hot or chemical or where the line tolerates the weep. Neither is the norm across the services these valves serve. (11.8)

NOTE A silent check is a valve that nobody sees working, which is both its virtue and its limit: it has no lever, no position indication, no cushion, and no adjustment, and it is selected on the strength of the manufacturer's spring selection alone. A spring too light lets the disc flutter at low flow and wears the guide; a spring too heavy costs head on every hour the pump runs. The deceleration on the valve schedule is what the manufacturer selects against, and the minimum pump flow is what keeps the disc off the stop. (11.10)

NOTE Requirements in this section apply to every dual-disc check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (12.1)

NOTE AWWA C518 is the waterworks standard for the dual-disc valve and carries the pressure rating, the materials, and the shell and seat tests that match the rest of a water plant's valves, which is why it is the default. API 594 describes the same valve for industrial piping, in the body materials and pressure classes of steel piping, and it is selected on a chemical, hot, or high-pressure industrial line where the AWWA materials do not serve. (12.3)

NOTE A resilient seat bonded in the body seals drop-tight on half discs that close under spring force and is the seat of nearly every waterworks dual-disc valve; a metal seat is chosen on hot and chemical industrial lines where no elastomer serves, and it weeps. Neither is the norm across the services these valves serve. (12.7)

NOTE The dual-disc valve puts the shortest laying length and the lowest weight of any check valve between two flanges, which is why it is the check valve of a process line in a crowded gallery. Its half discs close fast under their springs and its hinge pin carries the reverse pressure of both discs, so on a pump discharge it is a fast-closing valve with no cushion and no adjustment, and the surge analysis decides whether that closure is acceptable before it is scheduled there. (12.9)

NOTE Requirements in this section apply to every ball check valve furnished under this standard, whether selected in the datasheet for a service or designated for a particular valve on the valve schedule. (13.1)

NOTE A hollow steel ball with a vulcanized nitrile cover is the ball of nearly every sewage and sludge ball check, because its weight is set by the wall of the steel shell so that it sinks in the fluid and reseats by gravity, and its cover seals on grit and resists the grease. A solid elastomer ball is the ball of the small grinder station valve and of a chemical line, is lighter, and seats under reverse flow more than under its own weight. A phenolic ball is selected on hot or chemical lines where an elastomer cover does not serve, and it seals metal-to-resin rather than on a compliant surface. The ball is matched to the fluid's density as well as its chemistry, which is why no construction is defaulted. (13.4)

NOTE A ball check has no hinge, no pin, no spring, and no seat ledge for a solid to pack onto, and it clears itself on every cycle, which is why it is the valve of sludge and grit and of the pulsing discharge of a positive displacement pump. It is also the noisiest check valve made, because the ball lands on its seat on every stop, it does not indicate its position, and it accepts no lever, no switch, and no cushion, so a plant that wants to know whether a sludge pump is moving sludge looks at the pump rather than the valve. (13.8)

NOTE A foot valve sits wetted at the bottom of a wet well or a tank for its whole life and is reached only by pulling the suction pipe, so its material is chosen for the fluid it sits in rather than for the pressure it holds. Bronze is the body of the small foot valve in clean water and resists the biofouling of a raw water intake better than stainless. Type 304 serves treated water and Type 316 the chloride and sulfide of a wastewater wet well or a brackish intake. A coated ductile iron body is the economical body in the large sizes, with a stainless strainer because the strainer cannot be coated. No material is the norm across the intakes and wells this standard serves. (14.5)

NOTE The foot valve is what makes a suction-lift pump start: without it the suction pipe drains between runs and the pump has to prime itself on every start, which a centrifugal pump cannot do and a self-priming pump does at the cost of its seal. The strainer is what keeps the foot valve closing, because a stick across the disc is a pump that loses its prime every night. (14.7)

NOTE A slip-on duckbill is clamped over the outside of a pipe end and is the lowest-cost mounting and the quickest to replace, and it depends on the clamps alone to hold the valve against the reverse head. A flanged duckbill bolts to the pipe flange with a full-face elastomer flange of its own and holds the full reverse head through the bolts, which is why it is the mounting of a submerged outfall and of any discharge the tide stands on. A wall thimble or headwall mounting bolts the valve to the structure where there is no pipe end to mount on, as at a channel wall or an overflow weir discharging through a wall. The mounting follows the structure at each outfall rather than the valve. (15.4)

NOTE Neoprene is the compound most duckbill valves are molded in and resists the weather, the sunlight, and the seawater of an outfall; EPDM carries greater ozone and ultraviolet resistance where the valve is exposed above water, nitrile resists the oil and grease of a combined sewer or an industrial discharge, and chlorobutyl resists the chemistry of a treated effluent or a chemical drain. The manufacturer's standard compound serves the ordinary outfall, which is why the manufacturer's selection is acceptable, and a project whose discharge or exposure calls for another records it here. (15.6)

NOTE A duckbill has no moving part to foul and seals on a stone or a rag, which is why it is the check valve of an outfall that the tide, the river, or the receiving channel would otherwise back into the pipe. It opens a little under a small head and a lot under a large one, so the storm flow passes and the trickle does not drain the pipe, and its cost is a head loss at low flow that a steel flap gate does not have and a fabric body that is cut by a sharp object and by the sun. (15.9)

NOTE An outside lever and weight shows the disc position to anyone in the gallery, and on most plants that is all the indication a check valve carries. A closed-position switch tells the supervisory system that the pump has stopped moving water, which is the signal a station uses to detect a pump that is running against a closed valve or a valve that has not closed on a stop, and it is the switch most often bought. Open and closed switches let the system see the valve stroke on every start and stop, and a continuous transmitter lets it see a disc that is throttling on a pump running off its curve or a disc that is closing slowly as a hinge wears. The points a station reads follow its control narrative rather than the valve, which is why none is defaulted. (16.2)

NOTE Plated carbon steel is the bolting a valve ships with and serves a dry, heated gallery where it is inspected and painted with the valve. Type 304 holds up in the damp, hydrogen sulfide atmosphere of a wet well or a sludge gallery, where plated steel rusts within a few years and a seized cover bolt turns a seat replacement into a body replacement. Type 316 adds resistance to chlorides and is selected in a chlorinated water gallery, near the coast, or wherever the plant standardizes on it. The decision follows the atmosphere the valves sit in, which the project knows and the standard does not. (17.4)

NOTE Fusion-bonded epoxy is applied as a powder to a heated casting and cures into a hard, holiday-free film that bonds to blast-cleaned iron better than any liquid coating, and it is applied only in a shop equipped to heat the casting. Two-part liquid epoxy to the same standard is applied by spray in any coating shop and is the system a manufacturer uses where its castings are too large to heat. Both meet AWWA C550, both are certified to NSF/ANSI/CAN 61 by the manufacturers that offer them, and the choice follows the manufacturer's process rather than the project. A stainless steel, bronze, or aluminum bronze body and disc are not coated. (18.1.2)

NOTE The shop epoxy is a complete corrosion barrier on its own and is the finished exterior on a valve in a vault or a gallery where nobody looks at it. In a plant whose piping is color-coded or finished to a scheme, the valve exterior is topcoated in the field to match the pipe, and the shop epoxy becomes the primer that topcoat has to bond to. The decision follows the plant's finish scheme rather than the valve. (18.2.2)

NOTE A vault puts the cover, the lever, the dashpot, and the switches where a crew reaches them, which is the only way a lever-and-weight or a cushioned valve is adjusted after the trench is closed, and it is the access of nearly every buried pump discharge valve, at the cost of the structure and the confined-space entry it creates. Direct burial is the position for a free-swinging swing or flapper check on a yard line that is never adjusted and is dug up to be serviced, and it is chosen on a long yard main where a vault would be a structure for a valve nobody visits. The choice follows the valve's provisions rather than the project, which is why neither is defaulted. (19.2)

NOTE A check valve carries no operating nut, so no valve box, extension stem, or operating key is furnished for a buried check valve, and the valve box articles of the isolation valve standards do not apply to it. (19.6)

NOTE The seat test is applied in the reverse direction because that is the only direction a check valve ever holds, and a valve that passes its shell test and fails its seat test has a disc that is landing off its seat, a seat ring that is not seated in the body, or a hinge that is holding the disc up, all of which are found before shipment or in the wet well. (20.1.5)

NOTE A check valve's factory test is a shell test and a seat test on a product tested to a consensus standard in a factory with a quality system, and a certified report is what nearly every project accepts for it. Witnessing is bought for the large pump discharge valves whose closure response a project wants to see cycled with the dashpot set, and the valve schedule designates them. (20.2.2)

NOTE Rubber takes a set where it is compressed and left, and it degrades under ultraviolet light; a flapper valve stored closed in the sun for a construction season arrives at the line with a disc that has already lost the resilience it seals and hinges with. The manufacturer's shipping position relieves the seat, and the cover keeps the sun off it. (21.4)

NOTE A swing check installed in vertical piping with the flow downward hangs its disc open under gravity and never closes, and a swing check in horizontal solids service installed with its hinge at the bottom collects the solids on its disc and seat on every stop. The orientation is a property of the type, and the piping layout accommodates it. (22.1.5)

NOTE A check valve closes its disc against the flow pattern that reaches it, and a disc fed by the swirl off a pump elbow or a reducer flutters open and shut on every revolution, wears its hinge, and is still moving when the pump stops. The manufacturers publish the straight length each type needs, and a station too tight to provide it is the station where a nozzle check or a silent check with a shorter requirement is chosen. (22.1.8)

NOTE The weight on a lever is set at the factory from the manufacturer's experience and at the station from the station's own column, and the two are rarely the same. A stop with the weight too far in lets the disc slam; a weight too far out holds the disc partly closed against the running pump and shows up as a head the pump cannot make. The closure test on the real pump, under the real main, is where the number is found, and it is found before the station is in service rather than on the night the power fails. (22.3.6)

NOTE A check valve holds pressure in one direction, and the test pressure of the piping is set above the valve's rating by design. A check valve with the test on its upstream face opens and the test fails; a check valve with the test above its seat rating on its downstream face is damaged by the test it was never rated for. A blind flange is the test boundary, and the valve is tested free inside it. (22.4.3)

NOTE The cost that goes unassigned in a check valve warranty is never the valve. It is the pump that was lifted off its base by the slam, the main that split, and the wet well that flooded through a disc that did not close. Naming the slam at the recorded setting as a warranted failure is what makes the warranty worth having on a valve that cost less than the pump beside it. (23.6)

NOTE The seat, the flapper, and the ball are the parts a check valve wears, and the parts a crew replaces through the cover in an afternoon when the spare is on the shelf and in a month when it is not. A shaft seal set and a dashpot kit are held where the plant has levers and dashpots to service, and a spring and disc for a silent check are held where the plant has no other way to put a silent check back in service short of replacing it. (24.3)