I am having problems with a Spring seated check ball used in a low volume low flow (130 cubic in./min max) hydraulic device.

The device uses a .250" steel ball, 4.4 lb spring with a 54 lb/in spring rate, 118 degree included angle seat with a .0147 sq. in. contact area.

The original design intent was to prevent the actuation of the device until a pressure of 300 psi has been reached.

My problem is there appears to be a large pressure drop in the device after the check ball.

With the check ball installed the device engages at approx 640 psi.
With the check ball removed the device engages at approx 420 psi.

What could be causing the large 33.4% pressure drop, could it be caused by the spring rate?

Any ideas would greatly be appreciated.

What cracking pressure did you design the spring and ball combination for?  I.e. how much preload is in the spring when the ball is seated?

If your seat area is 0.015 in^2, or roughly a .14 inch diameter circle, and you put 4.4 lbs. of preload on the ball, then the cracking pressure should be roughly 300 psi.  That sounds fairly close to your number of 400 psi.  This is for a very low flow rate, when the ball has barely lifted from the seat.

With no spring or ball, the same orifice should produce a pressure drop of about 1 psi (using water as the reference fluid).  I'm assuming there is little or no restriction between the ball and the valve housing.

The ball and orifice together with a 54 lb/in spring should produce a bit more drop.  I usually use 20-30% of seat diameter as a rough opening distance for the ball, which gives a spring deflection of 0.2*.14 = .03 inch, or spring delta-force of .03*54 = 1.4 lbs, acting on the projected seat area of .015in^2 gives an additional 100 psi.  This is an upper ballpark for the flowing check valve.  There are published correlations for ball seats, but I've had trouble with the one listed in the Valve Designer's Handbook.

The others above have already in my opinion given you the answer, but let m try anyway:

It seems to me that you are trying to look at the pressure/forces on the ball for the different situations related to the fluid pressure contra the spring force (wich is again related to ball/spring travel) in 'static' situations

For a check valve you have normally three situations:

Situation 1: valve closed until a certain pressure; = cracking pressure.

Situation 2: valve fully opened at a given flow at a given pressure. This is the minumum flow/pressure to keep the valve fully opened.

Situation 3 : flow (and pressure)is 'in between' situation 1 and 2. . The flow is too low for the given reaction force (spring force compressed) to keep the valve completely opened. The ball is riding on a too low flow, or 'gulping' between closed and (partly)opened.

It seems to me that you could perhaps be in situation 3. This means the spring force is too high or the flow too low. In addition the partly opened system may restrict the flow further.

If your situation reaches a'no flow', but open valve situation, the pressure on all walls in two interconnected closed chambers would be equal.

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