Valve at inlet side of pump

[JBartlett]

Hi everyone, I'm thinking about building a piston type valve and placing it near the inlet side of a pump but my concern is that the piston may rise up due to suction at the inlet which I don't want to happen.

I'd really appreciate it if anyone could assess this drawing and determine if this would be the case.
I know suction causes the poppets in foot valves to rise up while the pump is running but does that occur because the poppet is facing parallel to the flow of water?
Could the piston rise up if it's facing perpendicular to the water flow or will this not happen?

 

[pointsman]

Is the pressure inside the suction pipe less than atmospheric pressure? If so you will have a pressure difference across the cylinder, creating a force pushing the cylinder into the pipe. This assumes that the exterior face of the piston is exposed to atmospheric pressure.

Conversely, if the pressure in the tube is greater than atmospheric, the piston would be forced out. You could solve all this by having an actuator of some kind which controls the position of the cylinder. The actuator (like your seals) needs to be beefy enough to resist the pressure differentials in play.

 

[LittleInch]

Why not just connect the moving valve bit to your actuator stem?

But agree - not enough is known about whether you can get a higher pressure on the other side of the moving piston. If it exposed to atmospheric pressure and not connected tot he actuator stem then yes, it could move.

 

[Doug Hunter]

There is definitely a risk of that, but it depends on the numbers. An alternative design would be a piston bore and piston that run across the opening, with a flow window in the piston. That would remove the axial force imbalance, but you might still have a lateral imbalance in the flow direction to resolve.

 

[JBartlett]

Is the pressure inside the suction pipe less than atmospheric pressure? If so you will have a pressure difference across the cylinder, creating a force pushing the cylinder into the pipe. This assumes that the exterior face of the piston is exposed to atmospheric pressure.

Conversely, if the pressure in the tube is greater than atmospheric, the piston would be forced out. You could solve all this by having an actuator of some kind which controls the position of the cylinder. The actuator (like your seals) needs to be beefy enough to resist the pressure differentials in play.

Yes, the pressure inside the valve will be lower than atmospheric pressure.
Could the weight of a piston prevent itself from lifting up in a lower pressure area? The weight of the piston is about 240 grams.

 

[pointsman]

Yes, the pressure inside the valve will be lower than atmospheric pressure.
Could the weight of a piston prevent itself from lifting up in a lower pressure area? The weight of the piston is about 240 grams.

In theory it could, but won't your valve have a control device (like a handle, or threaded stem) that controls the position of the valve? I think this would be a better solution that relying on the valve's weight to keep it in place.

Have you ever seen a valve that uses its weight to stay in position? I haven't. Very often there is a need to install valves in positions other than vertical, and then your solution to rely on the valve's weight would not work. Also, if the valves weight keeps the valve open, how do you close it?

 

[LittleInch]

whats the diameter of the piston?

You seem to know its weight, so can you provide all the information?

 

[JBartlett]

whats the diameter of the piston?

You seem to know its weight, so can you provide all the information?

Sorry, the diameter is 16.00mm.
Is there any other information you need?

 

[JBartlett]

whats the diameter of the piston?

You seem to know its weight, so can you provide all the information?

Length is 70.00mm

 

[Snickster]

Why not just do a force balance on the piston.

Forces acting down is pressure of suction in absolute times area of piston, plus weight of piston, plus any frictional force of piston against sides of cylinder.

Force acting up is the pressure on bottom of piston times area of piston which would be 14.7 psia if bottom side of piston is vented to atmosphere.