hand check valve VS check valve

[cranstonbu]

Wondering what is the difference between hand check valve and regular check valve. and their applications?

 

[gerhardl]

Hello cranstonbu:

If I have understood correctly 'hand operated checkvalve' is used (and in my opinion uncorrectly) to describe 'screw down non- return valves'. (Anyone : Please corrct me if I am wrong!).

Screw down non-return valves (which also can be motor or actuator operated) are checkvalves that will and can operate as normal non-return valves, under normal operational periodes. That is: the clack , disc etc. will close when fluid delta P over the valve reverses direction, closing for backflow of fluid in opposite direction to normal flow direction.

But: in addition to the normal operation by fluid force up and down, the valves can be forced to close down by the spindle screwed down: first part to overcome the free movement of the disc, and then (as a normal closing valve) forcing the closing element down and keep it permanently in closed position, until released by screwing up the spindle again.

Screw down non-return valves are far more seldom used than normal check-valves, as a high-quality non-return valve, correctly dimensioned and type-selected in most cases will be more then adequaate.

As a result screw down non-return valves are mostly used when the pipeline (or this part of the pipelin) is not in 'normal or regular use', and a backflow will have large consequences for instance for process, cost or environment.

Some applications and industries will have more 'normal' use of the screw-down non- return valves than others. For instance oil and gas (?).

 

[stanier]

A loose jumper stop cock is a "hand check valve'. You will find one in every garden, kitchen or toilet. The tap washer is loose inside the assembly. It stops reverse flow however the tap can be closed by hand to stop the flow in both directions.

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