Cast Steel Swing Check Valve: An Overview

A cast steel swing check valve is a self-acting non-return valve whose closure is a disc pivoting on a hinge pin; forward flow lifts the disc and reverse flow drops it onto the seat. Because it needs no stem, no packing and no actuator, it is the cheapest valve to keep in a line once it is installed, and the one most likely to be forgotten on the datasheet. The build on this page is cast ASTM A216 WCB to API 594 Type B (long-pattern, full body) in NPS 2 to NPS 24 and Class 150 to Class 2500, with ASME B16.34 carrying the pressure-temperature rating and ASME B16.10 the face-to-face length.

Specifications

The tabulated build runs from NPS 2 to NPS 24 in Class 150 to Class 2500, with Class 150 and Class 300 available from stock patterns and the higher classes cast to order. Sizes above NPS 24 move to ASME B16.47 flange drilling and are quoted on the drawing rather than from a table.

design standard

design features

1. Renewable seal welded seats with hard face

2. Internal hinge pin to minimize external leakage and ensure reliability in service.

Cast Steel Swing Check Valve drawing

Material of Construction

HF*：Hard-faced with stellite 6 or equivalent.

Note：Materials listed in the table are general. When ordering, please contact GNEE sales or technical team to confirm the details.

Face-to-Face: Long Pattern Matches the Gate, Short Pattern Drops into the Flange

ASME B16.10 fixes 698 mm at NPS 12 in Class 150 for a long-pattern swing check, which is the same length as the gate valve it replaces; the body is a full casting that lands between two flanges. API 594 also defines a short-pattern Type A wafer check whose body sits inside the flange gap - 38 mm at the same bore - and the two are not interchangeable, because the spool is welded to one length before anyone reads the drawing.

The short-pattern columns above are the API 594 Type A wafer dimensions, where the valve is clamped between the mating flanges and adds almost nothing to the spool length. A replacement ordered as a "swing check" with no pattern named is usually quoted as the long-pattern Type B, and it will not fit a line built for a 38 mm wafer body; the reverse also fails, because a 698 mm body cannot be closed by a flange gap of 38 mm. The pattern, not just the bore and class, belongs on the enquiry.

Pressure-Temperature Ratings

The table below is the carbon steel column of ASME B16.34 Table 2, Group 1.1, which is the group a WCB or A105 body is rated in. A Class 150 body holds 19.6 bar at 38 °C and 5.5 bar at 425 °C; the same casting in Class 600 holds 102.1 bar and 57.5 bar at the same two temperatures.

Two notes belong with this table. Note (1) of Table 2 states that carbon steel is permissible but not recommended for prolonged service above 425 °C, because the carbide phase can graphitise; the tabulated values above 425 °C exist but should not be used as a design basis. A WC6 or WC9 body is rated in a different group with a higher curve, and that is the substitution to make on a steam line, not a higher class in the same material.

Dimension & Weight

CLASS 150

CLASS 300

CLASS 600

CLASS 900

CLASS 1500

CLASS 2500

Swing, Lift or Dual-Plate: Which Check Valve

Three check-valve families share the non-return function and are not interchangeable, because each is built around a different closure element. The choice is made on the line orientation, the velocity and the slam margin, not on the pressure class, which all three cover.

The mistake this table prevents is a swing check specified where a lift or dual-plate valve belongs: a vertical-down line that needs a swing check to be spring-assisted, or a high-transient pump discharge that needs the spring and short stroke of a dual-plate valve rather than the long gravity swing. The pressure class is the same across all three; the closure element is what changes the application.

Test and inspection

send the line size, pressure class and quantity

FAQ

What standard covers a cast steel swing check valve?

A cast steel swing check valve is covered by API 594, with Type B describing the long-pattern full body in NPS 2 to 24 and Class 150 to 2500, and Type A the short-pattern wafer body. BS 1868 and API 6D are the alternatives for pipeline and general steel check valves, the body is ASTM A216 WCB, and the pressure-temperature rating comes from ASME B16.34.

Does a swing check valve need an operator?

No. A swing check valve is self-acting: the disc swings on a hinge and the line opens and closes it, so there is no stem, no packing gland and no actuator. The only items that change its behaviour are an optional spring, which sets the cracking pressure and allows any orientation, and an optional lever-and-weight or dashpot, which slows the closing stroke to control water hammer.

What is cracking pressure and why should it be specified?

Cracking pressure is the minimum forward pressure that lifts the disc off the seat, and it is the line most often left blank on a requisition. A bare swing disc cracks at about 0.02 to 0.05 bar by its own weight; a spring-assisted disc cracks at 0.1 to 0.7 bar and reseats against mild reverse flow. Without a stated value, an oversized valve can flutter against the seat at low flow and leak.

Can a swing check valve be installed vertically?

A bare swing check valve is installed horizontally with the hinge pin vertical, or vertically with upward flow only, because gravity must assist closing on reverse flow. It cannot be installed on a vertical-down run, where the disc is held open and the valve passes backflow; a spring-assisted disc is required for vertical-down or any-orientation duty.

How is a swing check valve different from a dual-plate check valve?

A swing check valve uses a single disc on a hinge pin, gives a low pressure drop on a full bore, and is the slam-prone choice on horizontal mains. A dual-plate check uses two spring-loaded plates in a wafer body, closes before the flow reverses, cuts slam by 60 to 80%, and fits any orientation including vertical-down, but it is a short-pattern body with its own face-to-face and class limits.

Is the face-to-face the same as a gate valve?

For the long-pattern Type B body, yes - a swing check valve is the same length as the gate valve it replaces, 698 mm at NPS 12 Class 150. The short-pattern Type A wafer body is a different matter at 38 mm at the same bore, and the two are not interchangeable because the spool is welded to one length before the valve is ordered.

What leakage class does a metal-seated swing check valve hold?

A metal-seated swing check valve is accepted at ISO 5208 Rate D, 0.1 × DN mm³/s, which is 30 mm³/s at DN 300, tested by the API 598 method as a differential across the closed disc. A renewable PTFE or NBR insert reaches ISO 5208 Rate A, effectively bubble-tight. A requisition written to "API 598 Class VI" or "FCI 70-2 Class VI" should be rewritten to the ISO 5208 rate before the order is placed.

Will a swing check valve cause water hammer?

A bare swing check valve is the most slam-prone non-return valve, because on a pump trip the disc is accelerated shut by reverse flow and strikes the seat, creating a surge. Slam is controlled with a long-radius disc, a lever-and-weight or dashpot, or by substituting a dual-plate or axial check whose spring closes the disc before the flow reverses. A bare swing check should be avoided on high-transient pump discharge unless it is damped.