API 594 is mainly used for dual plate check valve design and dimensional requirements, while API 598 is used for inspection and pressure testing. For a reliable RFQ, buyers should define the valve type, size, pressure class, material, seat, spring, end connection, service conditions, testing, and documentation.

What Is a Dual Plate Check Valve?

A dual plate check valve is a non-return valve used to prevent reverse flow in a pipeline. It has two spring-assisted plates that open with forward flow and close when flow slows down or reverses.

Compared with a swing check valve, a dual plate check valve is usually shorter, lighter, and easier to install in compact piping systems. It is commonly used in water, oil and gas, petrochemical, marine, power, and general industrial service. The key purpose is simple: allow flow in one direction and reduce the risk of backflow.

What Does API 594 Mean?

API 594 is commonly used for check valve design requirements, including wafer, lug, flanged, and butt-welding check valve types. For dual plate check valves, it is often referenced for body design, wall thickness, face-to-face dimensions, and construction requirements.

However, writing only “API 594 dual plate check valve” in an RFQ is not enough. The buyer still needs to define the body style, material, pressure class, seat type, spring material, and flange standard. Without these details, different manufacturers may quote different designs.

What Does API 598 Mean?

API 598 focuses on valve inspection and pressure testing. For check valves, it is commonly used to verify shell strength and seat leakage performance before shipment.

In practice, a dual plate check valve may be designed to API 594 and tested to API 598. These two standards serve different purposes, so both should be stated clearly when the project requires them.

API 598-related requirements may include shell pressure test, seat leakage test, test duration, inspection record, and acceptance criteria.

How to Specify the Right Dual Plate Check Valve

A good RFQ should start with service conditions. Before asking for price, define the medium, pressure, temperature, flow direction, installation position, and whether the valve will be installed horizontally or vertically.

Material should match the medium and temperature. Carbon steel may be suitable for many general services. Stainless steel, alloy steel, duplex stainless steel, or aluminum bronze may be needed for corrosion, seawater, high temperature, or special process conditions.

Seat and spring selection are also important. Soft seats may provide tighter shutoff in clean service, while metal seats are often selected for higher temperature or more demanding applications. Spring material should be checked carefully when the medium is corrosive or the valve is exposed to harsh service.

RFQ Checklist

Include the valve type, API 594 design standard, API 598 testing standard, size, pressure class, body style, body material, disc material, shaft material, spring material, seat type, end connection, flange standard, medium, temperature, pressure, installation position, leakage requirement, coating, and required documents.

At minimum, request a datasheet, general arrangement drawing, material certificate, inspection report, and pressure test report.

FAQ

What is the difference between API 594 and API 598?

API 594 is mainly for check valve design and dimensions. API 598 is for valve inspection and pressure testing.

Is a dual plate check valve better than a swing check valve?

It depends on the service. Dual plate check valves are compact and lightweight, while swing check valves may suit some low-velocity systems better.

What should I include in an RFQ?

Include service conditions first, then valve construction, materials, testing standard, leakage requirement, and documents.

Need Help Specifying a Dual Plate Check Valve?

Send your medium, pressure class, temperature, line size, body style, material, seat requirement, spring material, installation position, and testing standard. A technical selection can then be made based on the actual service conditions.