Swing Check Valve, Bronze, 1-1/4 in to 3 in FNPT, 150 PSI WOG

A swing check valve lets air travel one way and shuts the moment flow tries to reverse. On a compressor it is what stops a pressurised receiver from back-feeding the pump head every time the unit unloads or shuts down, and in a multi-compressor plant it is what stops one machine pushing air back through another that is sitting idle.

This is the classic Y-pattern bronze body: female NPT threads on both ends, a screwed bonnet cap on top, and a hinged internal disc that swings clear on forward flow and drops closed on reverse. Nothing to power, nothing to adjust, nothing to set. ACP lists these as "swing gate valves"; the industry name is a swing check.

Sizes and part numbers

• S1701: 1-1/4 in FNPT, 150 PSI WOG
• S1702: 1-1/2 in FNPT, 150 PSI WOG
• S1703: 2 in FNPT, 150 PSI WOG
• S1704: 2-1/2 in FNPT, 150 PSI WOG
• S1705: 3 in FNPT, 150 PSI WOG

The 1 in size in this same family is stocked separately as S1700.

Specifications

• Type: swing check, Y-pattern, gravity and back-pressure closing
• Connections: female NPT (FPT) both ends
• Maximum working pressure: 150 PSI WOG
• Body: cast bronze with a threaded bonnet cap
• Sizes: 1-1/4, 1-1/2, 2, 2-1/2 and 3 in

Sizing it

Match the valve to the pipe, not to the compressor nameplate. A check valve one size down from the line is a permanent restriction that costs you pressure every hour the compressor runs, and in a discharge line that pressure drop turns straight into wasted power. If the discharge pipe is 2 in, fit the 2 in valve.

Installing it

Orientation matters on a swing check. Mount it in a horizontal run with the bonnet cap upward, or in a vertical run only where flow travels upward. Never fit one in a vertical line with downward flow: the disc cannot fall closed against the flow direction and the valve will not seal. Check the flow arrow on the body before you thread it in, and support the pipe either side so the valve is not carrying the weight of the run.

On a compressor discharge, the check valve goes between the aftercooler or discharge pipe and the receiver inlet. Leave enough straight pipe ahead of it that the disc is not being hit by turbulence, and fit a union nearby so the valve can come out later without cutting pipe.

Service notes

A swing check that chatters or will not hold pressure overnight has usually picked up scale or carbon on the seat. Blow the system down, back the bonnet cap off and look at the seating face before you replace the whole valve. Checks on compressors that run hot carbon up faster than checks in clean dry service, so if this one failed early, look upstream at discharge temperature.

Related parts

We also stock in-tank check valves, pilot and unloader valves, ASME safety relief valves from 1/4 in to 1-1/4 in, automatic tank drains and Parker Watts air line filtration.

Bronze swing check valves for compressed air service in 1-1/4, 1-1/2, 2, 2-1/2 and 3 in female NPT, rated 150 PSI WOG, for compressor discharge lines and air receiver inlets.