NOTE This Standard covers general-duty valves furnished and installed in HVAC piping systems for isolation, shutoff, and non-modulating throttling service. (1.1)

NOTE General-duty valves are the manually operated isolation and throttling valves that punctuate every hydronic and steam distribution system: the gate valve at the base of a riser, the ball valve on a coil branch, the butterfly valve isolating a chiller, the swing check at a pump discharge. They are deliberately distinct from the automatic, actuated control valves that modulate flow to maintain a setpoint. A general-duty valve is either open or closed (isolation duty) or set once and left (coarse throttling duty); it is never expected to regulate flow continuously against a control signal. (1.2)

NOTE The systems addressed are hot-water heating, chilled water, condenser water, steam and steam condensate, and dual-temperature hydronic circuits. (1.3)

NOTE Boundaries with adjacent Standards. (1.4)

NOTE The following items are deliberately outside this Standard so that no device is specified twice and no service condition falls through a seam between Standards: (1.5)

NOTE Service-condition limit. (1.6)

NOTE Action Submittals. (3.1)

NOTE Informational Submittals. (3.2)

NOTE Closeout Submittals. (3.3)

NOTE Source quality. (4.1)

NOTE Standards compliance by valve type. (4.2)

NOTE Each valve family is governed by a specific MSS or ASME standard; specifying to the wrong standard invites a valve that is dimensionally or metallurgically inappropriate for the service. (4.3)

NOTE Regulatory basis. (4.4)

NOTE Design conditions govern valve selection. (5.1)

NOTE Every valve must be rated for the worst-case combination of pressure and temperature it will see in service — and on a hydronic system that worst case is not the pump head alone. It is the static head of the building column plus pump shutoff head plus any expansion-tank fill pressure, all evaluated at the system design temperature. The single most common field failure in this Standard's scope is a Class 125 cast-iron body specified against a system whose combined static-plus-pump pressure exceeds the 200 psig cold-water rating with no margin. (5.2)

NOTE Pressure-class ratings used in this Standard. (5.3)

NOTE The pressure classes below are the working envelopes used throughout this Standard. Steam ratings are saturated-steam ratings; cold-water (CWP / WOG) ratings apply at or below 65 °C unless the manufacturer's pressure-temperature table permits otherwise. (5.4)

NOTE Fluid and seat compatibility. (5.5)

NOTE Elastomer seat material must match the fluid. EPDM is the default for clean hot and chilled water and low-concentration glycol, but it swells and degrades in any petroleum-based fluid. Systems carrying oily steam condensate, or hydronic loops with glycol concentrations above roughly 50 percent or any oil contamination, require nitrile (BUNA-N) seats instead. (5.6)

NOTE Match the valve type to its duty. (6.1)

NOTE Each valve type exists because it does one job well. Choosing by familiarity rather than duty is the root of most valve RFIs: a globe valve used for simple isolation wastes pump head forever; a gate valve used for throttling erodes its seat; a wafer butterfly valve used as a dead-end isolation valve cannot be made to seal once the downstream flange is removed. The selection rules below assign each duty to its appropriate type. (6.2)

NOTE Default selections by service. (6.3)

NOTE The defaults below represent the 80 percent case across commercial and institutional HVAC. They are starting points, not mandates: the Engineer of Record may select otherwise where the service warrants. (6.4)

NOTE Body material follows size and service. (7.1)

NOTE Below NPS 2-1/2, bronze and brass bodies dominate hydronic and low-pressure steam service: they are economical, corrosion-resistant, and available in threaded and solder-joint ends. At NPS 2-1/2 and above, bronze becomes impractical — most manufacturers do not offer flanged bronze above NPS 3 — so the line transitions to cast iron, ductile iron, or steel. Ductile iron is selected over gray cast iron where higher mechanical strength or a Class 150 rating is needed; carbon steel is reserved for steam mains above 15 psig and for hydronic systems above 175 psig. (7.2)

NOTE End connections. (7.3)

NOTE End-connection type follows pipe material and joining method. Threaded and solder-joint ends are standard at NPS 2 and smaller; flanged ends are standard at NPS 2-1/2 and larger or wherever a flanged breakout is required for valve removal. Grooved ends apply where mechanical (coupling-style) piping is used. A critical and frequently missed detail: Class 125 cast-iron flanges are drilled to ASME B16.1 and do not share the bolt circle of Class 150 steel flanges to ASME B16.5 in sizes NPS 2-1/2 and NPS 3 — mixing the two without adapter flanges produces a joint that cannot be bolted. (7.4)

NOTE Gate valves. (8.1)

NOTE Gate valves provide full-bore, low-loss isolation but are unsuited to throttling: a partly open gate vibrates and erodes its seat. The principal selection question after material and class is stem orientation. An outside-screw-and-yoke (OS&Y) rising stem gives a clear visual indication of position and keeps the stem threads out of the fluid, but its travel demands vertical clearance — a real constraint in ceiling plenums and tight mechanical rooms, where a non-rising-stem or inside-screw valve, or a ball valve, may be required instead. (8.2)

NOTE Globe valves. (8.3)

NOTE Globe valves are the manual throttling and coarse-balancing valve of the corpus. Their tortuous flow path imposes a high pressure drop even fully open, which is the price of fine, repeatable throttling control and tight shutoff against a renewable seat and disc. (8.4)

NOTE Check valves. (8.5)

NOTE Check valves prevent reverse flow, most often at pump discharge where reverse rotation on shutdown can damage the pump and impeller. Swing checks are the default for horizontal lines; spring-loaded wafer or silent checks suit vertical-flow-up lines and locations where slam must be controlled. A check valve must be sized and oriented for the actual flow direction and mounting position — a swing check installed in a vertical-down line will not seat. (8.6)

NOTE Ball valves are the default small-line isolation valve. (9.1)

NOTE In NPS 2 and smaller, ball valves have largely displaced gate valves for isolation duty: they are lower in cost, quarter-turn (fast to operate, with obvious open/closed indication from the handle), and far more tolerant of frequent cycling. This Standard treats ball and gate valves as both acceptable for small-line isolation rather than mandating one. The principal ball-valve decision is port size. A full-port ball valve has a bore equal to the pipe ID and imposes negligible pressure drop; a standard- (reduced-) port valve is cheaper but obstructs the line and prevents rod-out. Full port is required in flow-critical and rod-out / pigging-service locations. (9.2)

NOTE Butterfly valves are the default large-line isolation valve. (10.1)

NOTE At NPS 2-1/2 and above, butterfly valves are the standard isolation valve for chilled-water, condenser-water, and hot-water mains: they are compact, light, and far cheaper than a flanged gate valve of equal size. MSS SP-67 distinguishes Type I (tight shutoff) from Type II (seating with allowable leakage); HVAC isolation duty calls for Type I. Two construction choices dominate selection — body style (lug versus wafer) and operator (lever versus gear) — and both have well-known failure modes if chosen carelessly. (10.2)

NOTE Body style: lug versus wafer. (10.3)

NOTE A wafer-body butterfly valve is sandwiched between two flanges and relies on both flanges staying bolted; remove the downstream pipe and a wafer valve can neither hold pressure nor be taken out without dropping the line. A lug-body valve has threaded (tapped) bolt holes on both flanges, so it bolts independently to each side and can serve as a dead-end isolation valve — the downstream side can be opened or removed while the valve holds the upstream pressure. Lug bodies are therefore mandatory at end-of-line, at equipment connections, and wherever the valve isolates a drainable section from the rest of the system. (10.4)

NOTE Operator selection. (10.5)

NOTE Resilient-seated butterfly valves have high breakaway torque because the disc edge must compress the elastomer seat. In small sizes a lever (handle with a notched plate) is adequate; in larger sizes the breakaway torque exceeds what one person can safely apply to a lever, and lever operation tears the seat and risks operator injury. A worm-gear operator with a handwheel multiplies torque and holds position. Gear operators are required at NPS 8 and larger by MSS SP-67, and are commonly specified from NPS 6 up for high-torque EPDM-seated valves. (10.6)

NOTE Operator type and reach. (11.1)

NOTE Valves mounted out of reach must be operable from the floor. Valves whose centerline is above roughly 7 ft above finished floor (AFF) require a chainwheel operator with a chain hanging within reach, unless a permanent platform or catwalk gives access. Selecting a chainwheel at design time avoids a field retrofit and the safety hazard of operating a high valve from a ladder. (11.2)

NOTE Drain and vent provisions. (11.3)

NOTE A drainable section needs a drain at its low point and a vent at its high point, or it cannot be emptied for service without improvised field connections — a recurring source of RFIs. Provide a hose-end (hose-bib) drain valve at system low points and at equipment isolation valve groups so the isolated section can be drained to a hose. Tee-head plugs serve where a hose connection is not needed. (11.4)

NOTE Valve tags. (12.1)

NOTE Every isolation and shutoff valve must carry a permanent tag keyed to the owner's valve schedule and P&ID, so an operator can find and identify a valve years after construction. Tags are stamped metal discs attached with wire or chain — adhesive labels are not acceptable in mechanical-room environments. (12.2)

NOTE Factory testing. (13.1)

NOTE Every valve is pressure-tested at the factory before shipment, and MSS SP-61 is the common test reference across all the valve types in this Standard. Two tests matter: the shell test, which proves the body and bonnet hold pressure with the valve partly open, and the seat (closure) test, which proves the closed valve does not leak past the seat. Acceptance leakage differs by type — bubble-tight (zero drops) for ball and gate valves, a defined allowance per ANSI/FCI 70-2 Class IV for globe shutoff valves. (13.2)

NOTE Field testing. (13.3)

NOTE After installation the valves are proved as part of the piping-system hydrostatic test, performed under Hydronic Piping. Valves are not the subject of a separate field pressure test; position and joint integrity are verified as part of the system test per the clauses below. (13.4)

NOTE Access and orientation. (14.1)

NOTE A valve that cannot be reached, read, or removed is a maintenance liability. Orientation matters: directional valves (check valves, some butterfly seats) follow the flow arrow, and butterfly discs need clearance to swing fully into the adjacent pipe. (14.2)

NOTE Isolation completeness. (14.3)

NOTE Insulation coordination. (14.4)

NOTE Protection before installation. (15.1)

NOTE Manufacturer warranty. (16.1)

NOTE Spares and consumables. (17.1)

NOTE Hand over the seat kits, packing, and operators the owner will need for routine maintenance, so a leaking stem or worn seat can be repaired without sourcing obsolete parts years later. (17.2)