Swagelok SS-4CP2-1 Poppet Check Valve, 1/4 in. MNPT, 1 psig

The Swagelok SS-4CP2-1 is the smallest, simplest way to stop backflow in a 1/4 in. line. It is a one-piece 316 stainless steel poppet check valve of the CP series with 1/4 in. male NPT ends on both sides, so it threads directly into female ports and needs no separate union. A fixed cracking pressure of 1 psig (0.07 bar) lets it open at very low inlet pressure and reseal as flow stops.

Technical specifications

One-piece construction

The CP series is a compact, one-piece body with a fully contained O-ring seal. In the larger C series the body is in two parts sealed by an O-ring with a backup ring, which adds length and leak paths; the CP removes that joint. The catalog lists the 4CP at a maximum Cv of 0.35 and says CP valves are rated to 3000 psig (206 bar) back pressure. At 1.62 in. in overall length with a 9/16 in. hex, the male-by-male version is one of the shortest check valves in the Swagelok range.

The poppet is spring-loaded: inlet pressure must exceed the cracking pressure to lift it and flow starts as a steady stream of bubbles. Reseal pressure is the pressure at which flow stops, and for the 1 psig valve the catalog gives the reseal as a back pressure up to 20 psig. For valves that have not been actuated for some time, the initial cracking pressure may be higher than the set value.

Ratings and flow

For 316 stainless steel valves with FKM O-rings the working pressure is 3000 psig from -10 F to 100 F, dropping to 2575 psig at 200 F, 2325 psig at 300 F and 2185 psig at 375 F. The catalog gives air and water flow curves for 1, 10 and 25 psi cracking pressures at various inlet pressures, so you can check the pressure drop at your flow. At 1 psi cracking, the valve starts to pass fluid at very low pressure and is therefore suitable for gravity-fed and low-pressure lines.

Other cracking pressures are available from Swagelok on request; the fixed CP series standard values are 1/3, 1, 10 and 25 psi.

Selecting a CP check valve

SS-4CP2-1 decodes as 316 stainless steel, 4CP series, end type 2 (male NPT) and cracking designator 1 (1 psi). End type 4 gives female NPT (SS-4CP4-), 5 gives male-by-female, and RT versions give ISO tapered threads. Replace the designator for other cracking pressures: -3 on the adjustable CPA series covers a 3 to 50 psig range. Brass versions use B in place of SS. Select the valve for the fluid and note that check valves are not leak-tight shutoff devices; do not rely on them as isolation.

Install with the arrow pointing in the flow direction, seal the tapered threads, and fit a filter upstream in dirty service because particles on the poppet seat prevent resealing.

Documents and quotation

The attached Swagelok check valves C, CA, CH, CP and CPA series catalog MS-01-176 (EN, rev. N) is the reference for every value on this page. Seven Star LLC, an independent supplier in Muscat, quotes SS-4CP2-1 against the exact code; please add the quantity and any special requirement.

We recommend confirming the exact size, thread standard and material with the attached document before placing an order. Related items: product category.