swing check valve and surge - Valve engineering

The best way to answer is in my opinion to recommend the best possible installation: two valves (one checkvalve and one emergency shutdown valve) that can work independently of each other, without the one or the other disturbing the function of the second.

You need:

a) To avoid slamming by pressure peaks:

A checkvalve that closes when delta p is zero, or more correctly spring operated closing, marginally before delta p is zero. Best choice: non-slam soft closing nozzle check valve. Or, second choice, but depending on size and pressure class: disc (not swing) check valve with spring. Both valvetypes from top quality manufacturors.

Another choice might be tilting disc with counterweight, with hydraulic piston damping.

This third alternative will require exact flow data (all possible situations!) at all times to dimension the solution. Same is valid for the two others, but with larger limits for accuracy.

b) An emergency shutdown valve with regulation (setting) possibillities for the closing down time stroke, preferably if large size: fast for (say) first 70-80%, slower for rest.

Dimensioning is necessary both for size and closing time (both for one and two-step closing) to prevent hammerblow pressurepeaks backpressure.

The whole piping construction need to be considered for correct dimensioning and placement of alll components.

Direct answer to your questions:

1. Yes, but only if dimensioned correct, mounted correct and best with spring assistance, and only under certain hydraulic conditions (flow amount) and limits. In practice it will more likely have a very good chance of closing with a 'bang'.

You will often see swing check valves damaged with pin and hinge or sealing problems. This is caused by one or more of following causes: bad/weak construction, wrong dimensioning or mounting (placement) causing sudden closing creating shockwaves and repeating hammerblow closing (or 'gulping'-opening closing rapidly ande repeatedly- if too large for flow or throtteled flow).

2. Yes, but see point 1.

Good luck!

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Piston Check

A piston check is very similar in function to a lift check. The big difference is that the disc is spring loaded, meaning that a spring pushes the disc into a closed position. This closes the disc faster, causing less backflow in the line and reduces the possibility of hammer-stop. However, it can also result in a higher amount of pressure reduction since the flow pressure has to both lift the disc and press the spring-loaded piston upward.

Inline Check

Inline check valves are smaller-bodied check valves that are spring loaded. Most inline check valves are intended for vertical installation, though they can be used in any direction. It has a disc or globe inside of it that is forced by a spring to seat in the inlet, stopping backflow. Flow pressure against the disc or globe in the correct direction causes it to open, and when pressure begins reducing, the spring presses it back into a closed position again. This is great when a check is needed and flow is moving in a downward vertical direction because the check does not rely on gravity or solely on backflow pressure to close.

This style is also known as a silent check. The reason for this is that the spring pressure causes it to close gradually and directly as inflow pressure reduces which results in a quieter close. A silent close means less hammer-stop and less vibration, which means pipes and valves last longer.

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