Eccentric Plug Valves

NOTE This standard covers the resilient-seated eccentric plug valve: a quarter-turn valve whose plug rotates on a shaft offset from the seat so that the plug lifts out of the flow path when it opens and presses into a raised seat when it closes, built to AWWA C517 in sizes 3 in. through 72 in. for raw water, wastewater, sludge, scum, grit, and other liquids that carry solids. (1.1)

NOTE The boundary of the work is the valve from face to face, with its manual operator or its mounting base for a power actuator, its lining and coating, and the extension stem and valve box of a buried installation. The piping the valve sits in, the pipe supports, and the actuator that drives it from the control system are governed by the standards named for them. (1.2)

NOTE A gate valve in a sludge line closes into the grit that has settled in its seat, and a ball valve traps solids in its cavity. The eccentric plug valve is specified in solids service because the plug swings clear of the port when it is open and seats without wiping across the body, so a settled solid is pushed aside rather than packed into the seal. The orientation rules in this standard exist because that advantage depends on how the valve is installed, not only on what it is. (1.3)

NOTE Valves in this standard are isolation valves. A plug valve that modulates against a process variable, with the positioner and actuator that duty requires, is a control valve under Control Valves And ActuatorsControl Valves and ActuatorsResolves to the current adopted revision.sync/control-valves-and-actuators, and the electric, pneumatic, or hydraulic actuator mounted on an isolation valve under this standard is furnished under Valve And Gate ActuatorsValve and Gate ActuatorsResolves to the current adopted revision.sync/valve-and-gate-actuators. (1.5)

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, the umbrella for the process discipline, and the valve is installed in piping governed by Ductile Iron Process PipingDuctile Iron Process PipingResolves to the current adopted revision.sync/ductile-iron-process-piping, Steel And Stainless Process PipingSteel and Stainless Steel Process PipingResolves to the current adopted revision.sync/steel-and-stainless-process-piping, or Plastic Process PipingPlastic Process PipingResolves to the current adopted revision.sync/plastic-process-piping inside a plant, by Water Distribution PipingSite Water Distribution PipingResolves to the current adopted revision.sync/water-distribution-piping on a buried site water main, and by Sanitary Sewer SystemsSanitary Sewer Systems (Site)Resolves to the current adopted revision.sync/sanitary-sewer-systems on a sewage force main. (1.6)

NOTE The following are outside this scope and are governed by the standards named. (1.7)

NOTE The orientation shop drawing is the submittal that catches the most errors on this product, because a plug valve that is correct in every material and rating still fails in solids service when its shaft is vertical or its seat faces the wrong way. Reviewing the orientation on paper, valve by valve, is far cheaper than finding it in a sludge line. (3.1.3)

NOTE A plug valve in a treatment plant is serviced in place for decades, and the part that wears is the plug facing. A manufacturer that can still supply a plug for a thirty-year-old body is what keeps a seal replacement from becoming a valve replacement with a piping modification around it. (4.1.4)

NOTE The stop settings on an eccentric plug valve are what put the plug on the seat without driving it past, and they are set against the actual plug and seat the valve shipped with. An actuator mounted in the field is set by a party that did not build the valve, against a seat it cannot see. (4.2.4)

NOTE A valve on a raw water line ahead of a drinking-water plant, or on finished, backwash, or reclaimed water, is a drinking water system component to most regulators, and the certification is what the regulator and the utility accept as proof. A valve on wastewater, sludge, or scum carries no such requirement, and a certified lining costs more and narrows the list of manufacturers. The decision follows the service of the valves on the project, which is why the field has no default. (4.3.3)

NOTE The body of a closed plug valve holds a pocket of line fluid on each side of the plug that does not drain with the pipe. Where that fluid can freeze, the pocket is the part of the line that breaks, and the piping standard's freeze provisions have to reach the valve body, not stop at the flange. (5.2.3)

NOTE Valves smaller than 3 in. in process service are outside AWWA C517 and this standard, and the piping standard governing the line selects the small valve. (6.1.3)

NOTE AWWA C517's minimum port area is a fraction of the pipe area, about 80 percent for most sizes, and the standard-port valve built to it is the valve most manufacturers stock and most plants own. Its head loss is small in isolation service, where the valve is either open or closed. A full port valve costs more and has a longer body, and it is selected where the line is pigged or cleaned with a tool that has to pass through the valve, where the valve is throttled in a fixed position and the loss across the reduced port would matter, or where a sludge line is sized tightly enough that the port reduction would raise the velocity at the valve above what the solids tolerate. The choice follows the lines on the project rather than the product, so the field carries no default. (6.2.4)

NOTE AWWA C517 rates valves 12 in. and smaller at 175 psi and 14 in. and larger at 150 psi, and that rating covers nearly every raw water, wastewater, and sludge line a treatment plant has. Where a force main or a high-head pump discharge is designed above it, manufacturers offer heavier bodies in the smaller sizes, which is why the field is derived from the size and the piping design pressure rather than fixed at the standard's number. (6.3.4)

NOTE Line pressure that reaches the plug from the side opposite the seat presses the plug into the seat, and the valve seals more tightly as the pressure rises. Pressure that arrives from the seat side tries to lift the plug off, and the seal then depends on the operator's seating force and the elastomer's interference alone, so the reverse rating of a valve is often well below its direct rating. A bidirectional valve carries a seat and a seating load that hold either way, at a higher operating torque and price. The decision is a matter of where the pressure comes from when the valve is closed: a valve that always closes against one direction, such as a tank outlet, is served by a direct-pressure valve installed the right way round; a valve that sees pressure from both sides, such as a pump discharge that holds back the force main when the pump is off and holds back the pump when it runs against a closed valve, or any valve whose line can be pressurized from either end for maintenance, needs the bidirectional rating. (6.4.4)

NOTE Cast iron is the material AWWA C517 is written around and the body nearly every plug valve in a treatment plant is cast in, at the lowest cost and with the full size range available. Ductile iron carries roughly twice the tensile strength and a ductility that cast iron lacks, so it is selected where the valve is rated above the standard pressure, where it is buried in a line subject to ground movement or heavy surface loads, or where a flanged body is bolted to a steel flange and the bolting load would overstress a gray iron flange. (7.1.4)

NOTE The plug is the part that carries the seating load and the operator's torque, and a plug in a large valve sees a bending moment across its full width every time it closes against pressure. Ductile iron carries that moment with margin and is the material most manufacturers cast large plugs in; cast iron is lighter and less costly in the small sizes, where the moment is small. The two castings are independent choices because a cast iron body with a ductile iron plug is a common and sound combination. (7.2.3)

NOTE Chloroprene is the facing the eccentric plug valve was developed around and is the standard offering for raw water, wastewater, and sludge, with a long service record against sewage and a modest resistance to oil. Nitrile holds up against the grease and petroleum oils that reach a scum line or an industrial sewer and is the facing selected where those are present. EPDM carries the highest water-service temperature of the common facings and resists chlorine and chloramine, which attack chloroprene and nitrile over years of contact, so it is selected on chlorinated and chloraminated water. Chlorosulfonated polyethylene resists ozone and oxidizing chemicals. Fluoroelastomer carries the broadest chemical resistance and the highest temperature rating at the highest price, and is selected where the line carries a chemical the others cannot tolerate. (7.2.6)

NOTE The seat is the one metal surface the plug facing bears on, and the raised seating surface of a plug valve is in the flow when the valve is open. A welded-in nickel overlay is corrosion resistant against the full range of sewage chemistry, fused to the body so there is no joint for grit to work into, and it is what AWWA C517 valves have carried for decades. A stainless overlay serves the same purpose where the owner standardizes on stainless wetted parts. A retained seat ring can be replaced in the field when it is scored, at the cost of a joint between ring and body that the line fluid can reach, which matters most in grit service. (7.3.5)

NOTE The shaft seal is where a plug valve leaks to the outside, and in a gallery the leak is sewage on the floor. Self-adjusting V-type packing keeps its seal as the elastomer wears without anyone touching it, which is why it is the standard offering. Adjustable packing lets an operator take up a leak with a gland nut and suits a plant whose staff prefers to maintain the seal rather than replace it. U-cup seals carry the lowest friction and are selected on power-actuated valves where the seal's drag is a share of the actuator torque. (7.4.5)

NOTE Flanged ends are the connection of exposed plant piping, where the valve is bolted between flanges it can be unbolted from for service, and they are the standard offering in every size. Mechanical joint ends take the restrained gasketed joint of a buried ductile iron main and let the valve be assembled in the trench without flange alignment, and they are the connection of buried service. Grooved ends suit a grooved process piping system in the sizes the coupling manufacturer rates for the line pressure. Threaded ends are available only in the smallest size and suit a threaded sludge or drain line where a flange would not fit. (8.1.3)

NOTE Class 125 drilling matches the flanges of every ductile iron fitting and flanged pipe in a plant and every cast iron valve, 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. (8.1.7)

NOTE Plated carbon steel is the bolting a valve ships with and is adequate in 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 seal 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. (8.2.4)

NOTE Both epoxy systems comply with AWWA C550 and both are standard offerings, which is why the manufacturer's choice is acceptable. Fusion-bonded epoxy is applied as a powder to a heated casting and cures into a hard, uniform film that resists abrasion from grit, and it is the system most plug valves are lined with. Liquid epoxy is applied cold and suits a repair, a touch-up, or a casting too large for the manufacturer's oven. A thicker film buys abrasion life in grit and sludge service and holiday-free coverage on a rough casting, at a cost in cure time and in the risk of sagging on vertical surfaces. (9.5)

NOTE A lever is the fastest operator a plug valve can have, a quarter turn from open to closed, and in the small sizes the operating torque is low enough for one person to close it against rated pressure. At 6 in. the torque in sludge service is at the edge of what a lever can deliver, and a lever that cannot be moved by hand gets a pipe extension put on it. A worm-gear operator trades speed for a rim pull anyone can apply and for a self-locking gear train that holds the plug where it is set, so a plant that throttles its small plug valves in a fixed position, or whose operators work from a platform, tends to specify gears down to the smallest size. (10.1.2)

NOTE A handwheel is the operator of a valve at an operating floor, where the operator stands at it. A chainwheel is the operator of a valve mounted overhead, and it is selected per location rather than per project. A 2 in. square operating nut is the input of a buried valve and of an exposed valve the plant operates with a portable wrench or key, and a handwheel fitted with a nut lets the same valve be operated by hand at the floor and by a portable actuator when the pull is heavy. (10.2.4)

NOTE Eighty pounds is the rim pull the AWWA valve standards have long used as the limit a person can apply to a handwheel, and it is the figure nearly every waterworks specification carries. A lower limit buys an easier valve at the cost of a higher gear ratio and more turns from open to closed, and it is selected where the operators work from a ladder or a platform, or where a plant standardizes on a lower figure. (10.2.7)

NOTE Counterclockwise to open is the AWWA default and the direction nearly every plant and utility operates, and a valve that opens the other way is a valve an operator will close when they mean to open it. Clockwise to open is selected only where the owning utility has standardized on it across its system, so that every valve the same crew touches turns the same way. (10.2.9)

NOTE Electric motor actuators under AWWA C542 and pneumatic and hydraulic cylinder actuators under AWWA C541 on valves under this standard are furnished and specified under Valve And Gate ActuatorsValve and Gate ActuatorsResolves to the current adopted revision.sync/valve-and-gate-actuators; the actuator of a plug valve in a modulating control loop is furnished under Control Valves And ActuatorsControl Valves and ActuatorsResolves to the current adopted revision.sync/control-valves-and-actuators. (11.2)

NOTE The torque of an eccentric plug valve rises with the differential pressure, with the seating interference of the facing, and with the time the valve has sat closed in sludge, and the figure that matters for the actuator is the breakaway torque at the rated differential after that sit. A valve that is sized from running torque alone stalls its actuator the first time it is asked to open against a full force main. (11.5)

NOTE A valve box is the lowest-cost access, a cast iron shaft from the operator to a lid in the surface, and a crew operates the valve from grade with a key. It suits an isolation valve that is operated a few times a year and needs no inspection. A vault puts the operator, the shaft seal, and the flanges where a person can reach them, and it is selected for a valve that is operated often, that carries a power actuator, or that sits where a leak at the seal has to be seen before it reaches the ground, at the cost of the structure and the confined-space entry it creates. (12.3)

NOTE A shallow nut lets a short key reach it and a crew see the nut before engaging it; a deep nut needs a longer key and a crew working blind. Utilities that operate many valves tend to set a shallow limit; a plant with a few buried valves on deep force mains tends to accept a deeper nut rather than a long stem that whips in the box. (12.5)

NOTE A valve box that bears on the valve transfers wheel loads and settlement from the surface into the body and the main, and a box that is off plumb binds the key at the lid and the stem at the nut, so the valve box is set on compacted backfill and checked plumb before the surface is finished. The buried valve is the one valve nobody sees after the trench is closed, and the box is the only path to it. (12.8)

NOTE A certified report is what nearly every project accepts for a product tested to a consensus standard in a factory with a quality system, and a witnessed test adds travel and a factory hold for each lot. Witnessing is selected where the valves are large, where the project carries a bidirectional rating or a pressure above the standard rating that the Engineer of Record wants to see proven, or where a prior project with the same manufacturer found a seat leak after delivery. (13.5)

NOTE A plug that opens downward swings into the bottom of the body, where the solids that drop out of the flow settle, and it closes by lifting through that bed of grit every time. A plug that opens upward stores above the flow where nothing settles on it, and the solids collect in the bottom of the body where the seat is not. A vertical shaft puts the lower bearing in the sediment and the plug's travel in the same plane the solids settle in, which is why the shaft is horizontal in solids service whatever the piping layout prefers. (14.1.3)

NOTE A pump discharge isolation valve is closed so the pump can be serviced, and while it is closed the pump is off and the force main's static head is on the far side of the plug. Orienting that valve for the running condition, with the pump pressure on the seat, seals it while the pump runs and lets it weep onto the open pump while the mechanic works on it. The closed condition that matters is the one the valve is closed for. (14.1.6)

NOTE A cast iron valve flange bends across the edge of a misaligned mating flange as the bolts are tightened, and cast iron has almost no ductility to absorb the bending. The crack appears at the valve, and the valve is blamed for a piping error. (14.2.2)

NOTE A valve that forms a piping test boundary is being asked to hold the test pressure on its seat, and the test pressure of the piping is set above the valve's rating by design. A direct-pressure valve with the test on the wrong side of the plug leaks, the test fails, and the valve is blamed; a bidirectional valve with the test above its seat rating is damaged by the test it was never rated for. A blind flange is the test boundary, and the valve is tested open inside it. (14.3.4)

NOTE A plug valve lifted by its operator carries the full weight of the body through the operator's mounting bolts and the shaft, and the stops and the indicator that were set at the factory are the first things to shift. The valve arrives on site looking undamaged and closes past its seat on the first cycle. (15.4)

NOTE An elastomer facing held against its seat under full interference for months takes a set at the seat line that it does not recover from, and the valve then seals at that one position and weeps at every other. Storing the valve open keeps the facing unloaded. (15.6)