Lift check valve

Lift Check Valve PN40 1.Size:DN15~DN100 2.Valve body:CF8M 3.CE,ISO9001Certificate

The lift check valve consists of four main components: the body, a disc, a spring and a spring retainer. The disc moves in a plane at right angles to the flow of the fluid, resisted by the spring that is held in place by the retainer. The body is designed to act as an integral centring collar that facilitates installation. Where a 'zero leakage' seal is required, a soft seat can be included.

Fig. 12.3.3 A disc check valve

When the force exerted on the disc by the upstream pressure is greater than the force exerted by the spring, the weight of the disc and any downstream pressure, the disc is forced to lift off its seat, allowing flow through the valve. When the differential pressure across the valve is reduced, the spring forces the disc back onto its seat, closing the valve just before reverse flow occurs. This is shown in Figure 12.3.4. The presence of the spring enables the disc check vale to be installed in any direction.

Fig. 12.3.4 Operation of a disc check valve

The differential pressure required to open the check valve is mainly determined by the type of spring used. In addition to the standard spring, there are several spring options available:

No spring - Used where the differential pressure across the valve is small.Nimonic spring - Used in high temperature applications.Heavy-duty spring - This increases the required opening pressure. When installed in the boiler feedwater line, it can be used to prevent steam boilers from flooding when they are unpressurised.

As with all wafer check valves, the size of the disc check valve is determined by the size of the associated pipework. This usually ensures that the valve is correctly sized, but there are cases where the valve is over or undersized.

An oversized check valve is often indicated by continuous valve chatter, which is the repeated opening and closing of the valve that occurs when the valve is only partially open. It is caused by the fact that when the valve opens, there is a drop in the upstream pressure; if this pressure drop means that the differential pressure across the valve falls below the required opening pressure, the valve will slam shut. As soon as the valve shuts, the pressure begins to build up again, and so the valve opens and the cycle is repeated.Oversizing can usually be rectified by selecting a smaller valve, but it should be noted that this will increase the pressure drop across the valve for any one flow. If this is not acceptable, it may be possible to overcome the effects of chatter by reducing the closing force on the disc. This can be done either by using a standard spring instead of a heavy-duty one, or by removing the spring altogether. Another alternative is to use a soft seat; this does not prevent the chatter but rather, reduces the noise. Care must be taken however, as this may cause excessive wear on the seat. Undersizing results in excessive pressure drop across the valve and, in the extreme, it may even prevent flow. The solution is to replace the undersized valve with a larger one. Disc check valves are smaller and lighter than lift and standard swing check valves and subsequently cost less. The size of a disc check valve is however limited to DN125; above this, the design becomes complicated. Typically, such a design would include a cone shaped disc and a small diameter spring that is retained and guided along the centre line of the cone, which is more difficult and expensive to manufacture. Even then, such designs are still limited in size to DN250.Standard disc check valves should not be used on applications where there is heavily pulsating flow, for example, on the outlet of a reciprocating air compressor, as the repeated impact of the disc can lead to failure of the spring retainer and high levels of stress in the spring. Specifically designed retainers are available for such applications. These designs typically reduce the amount of disc travel, which effectively increases the resistance to flow and therefore increases the pressure drop across the valve. The design of disc check valves allows them to be installed in any position, including vertical pipelines where the fluid flows downwards.

Different styles and sizes are ok,Customer's need is first.

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Lift check valve