Valve

[davyjacob]

Hello!

I am looking for a non return valve(NRV) which is connected in series.
The flow is allowed to flow only in one direction.
For eg, NRV 1 connected in series with NRV 2. (diaphragm or spring NRV)
Let us say I am taking both NRV 1 and NRV 2 as a spring type.
Stiffness of NRV 1 is less while the Stiffness of NRV 2 is more.
Fluid flows from the end NRV 1 to NRV 2.
Pressure generated at the end of NRV 1 is capable of opening NRV 1 but this pressure is not enough to open the NRV 2.
I cannot use the stiffness for NRV 2 as same as NRV 1 because the pressure generated opposite to the fluid flow at the end of NRV 2 is more.
As you can see in my case I want some mechanism in such as way that the pressure at NRV 1 amplifies and reaches the NRV 2 inorder to open NRV 2 and to allow the flow.
This is something like a lever where a small force is applied to lift a larger mass.

How this can be done? ANY IDEAS?

If there is any other valve available to do this process please reply.

 

[gerhardl]

I do not think I am understanding your question.

Call upstream necessary opening pressure for NRV 1 for 1P1, and downstream existing pressure for NRV 1 for 1P2. Likewise for NRV2, 2P1 and 2P2. To open the valves real upstream pressures will always have to reach the level of the opening pressure (set by selected spring in this case). To start a flow you have to have a situation where 1P1 > 1P2. To have a flow from 1P2 further downstream past NRV2 : 1P2 > 2P1 > 2P2. You can not create a flow against a negative pressure difference (P1<P2).

If you want to supply fluid upstream from NRV2 to a higher pressure downstream (2P1 > 2P2) you can do this three ways:

a) Create a higher pressure between valves 1 and 2 by adding more fluid at higher pressure (pumping, connect reservoir or source at higher pressure). The fluid can be the same as the original, or you can add gas (air?).

b) Create a higher pressure by mechanically reduce the volume between 1 and 2 (piston, volume in rubber bag pressurized from outside etc, rubber bag inside reservoir filled up with air/gas at higher pressure etc.) to reach a higher pressure this way.

c) Use another type of valve closing and opening by hand or motor. If opened :flow will go from downstream to upstream to mix the fluids.

Other options will exist if 2P2 or otjher pressures decreases or varies over time, and overflow or regulating valves operated by pilots may be used in different ways. Flow direction will always be from higher to lower pressure.

Please forgive me if I have not grasped your problem fully. Further details from you might give more help.

 

[LittleInch]

Davyjacob,

You've answered your own question.

" I want some mechanism in such as way that the pressure at NRV 1 amplifies and reaches the NRV 2 inorder to open NRV 2 and to allow the flow.".

This is called increasing the pressure upstream of nrv1. As gerhardl says, if the pressure p1 < p2, you won't get flow in the positive direction.

Also be aware that what you are referring to is really pressure relief valves. NRV springs are not good at providing resistance to a reliable and repeatable level. They are simply there to close the nrv when there is very little reverse flow.

Also if you're talking liquid, nrv1 may not actually open as the liquid downstream is in compressible.

Think a little more about what you're trying to achieve as your scheme doesn't sound correct to me.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way