Q1. What is a forged steel welded check valve used for, and where is it used?
A1. A check valve prevents reverse flow and does nothing else — it is not an isolating valve and cannot be used to shut a line down. It is fitted wherever backflow would damage equipment, contaminate a line or drain a header: at the discharge of every pump, on compressor and blower outlets, on the suction of a pump fed from a pressurised source, downstream of a meter, at the outlet of a boiler feed line, and on any branch that must not drain back. It works automatically, with no operator and no external signal, so it has to be chosen so that it neither chatters at low flow nor slams when the flow reverses. Because it is a passive item with no adjustment once it is in the line, its closing behaviour is what decides whether it protects the line or damages it. In forged construction it is used on small-bore high-pressure duty — steam and instrument lines, and services where a sound, radiographically clean body is required.
Q2. What design variants are available, and how do I tell them apart?
A2. The type is chosen from how much space is available and how fast the flow reverses. A swing check has a hinged disc and is the most common on water and steam mains, but it needs a long installation length and its disc can slam. A dual-plate (wafer) check puts two spring-loaded half discs in a short body, which suits tight spaces and reduces slam. A lift check guides the disc vertically and is used on high-pressure small-bore lines and where the flow is always in one direction. A tilting-disc check is the answer on large compressor and pump discharges, because the disc closes before the flow has fully reversed. Nozzle or axial checks use a spring-loaded ring around the axis and are chosen where the response has to be very fast.
Q3. What has to be confirmed before a valve is welded into a line?
A3. Three things. The pipe grade and wall thickness that will be welded to the valve end, because the end preparation has to match the schedule. The welding procedure that will be used, which has to cover both materials of the joint and be qualified. And the pressure class at design temperature, which sets the wall thickness on the valve side. A mismatch found on site is expensive: cutting out a welded valve damages the end preparation and usually costs more than the valve itself.
Q4. How is the valve pressure tested before delivery?
A4. Every valve is shell-tested and seat-tested before dispatch. The shell test is at 1.5 times the rated pressure at 38 °C with the valve partly open, proving the pressure boundary; the seat test is at 1.1 times with the valve closed, proving the closure. Holding time follows the standard and the size. Acceptance is normally quoted against ISO 5208: Rate A means no visible leakage, while lower rates permit a defined leakage over the test period. The rate that applies should be written into the specification — on gas, toxic or metered service Rate A is the usual requirement.
Q5. What is the difference between a forged body and a cast body?
A5. A forged body is formed from solid bar or billet under pressure, so the material is worked and its grain flows around the shape instead of being cast into it. There are no shrinkage cavities or gas pores, and the part can be examined volumetrically — radiographic or ultrasonic — and traced as a single piece of known origin. That is why forged bodies are used on small-bore high-pressure duty — steam and instrument lines, hydrogen and ammonia service, and the higher classes where casting quality is harder to assure in a thick wall. A casting is cheaper and allows a more complex internal shape and a larger bore, and in the common sizes at standard classes the quality is well controlled by the casting standard and by radiographic examination. The working rule is that small and thick-walled goes to forging, large and complex goes to casting.
Q6. How do I select the right one for my line?
A6. Selection starts from the service, not from the catalogue. Fix the medium and its concentration first, because that decides the body material and the seating. Then the design pressure and the design temperature together, since the allowable pressure at temperature is lower than the cold rating and it is the hot figure that governs. Then the size, the connection, and how often the valve will be operated, which is what decides between a handwheel, a gearbox and an actuator. Bring those five answers to the enquiry and the rest of the selection follows from them.
Q7. How do I order, and what information is needed for a quotation?
A7. Ordering starts from the line list: tag number, size, class, medium, temperature, connection and operating method. Send that and we will confirm material and seat selection against the medium, flag anything that is likely to cause trouble on site, and quote accordingly. Special sizes, operators and materials are produced to order.
