Pressure drop in hydraulic fluid for a change in volume

[Roylance]

Greetings,
This seems on the face of it a simple problem but for the life of me I can't seem to get a grip on it.
I want to determine the pressure in a system after the system's volume has increased. Basically, a predefined volume has it's pressure increased to a certain pressure when this pressure activates a mechanism allowing a piston to stroke which results in a relatively small increase in the system volume.
The medium is hydraulic fluid. My main struggle is how to account for the bulk modulus of the fluid in the calcs.
Any pointers would be greatly appreciated!

 

[Roylance]

I think I may be answering my own question now so it's more a case of getting some corroboration that I am not barking up the wrong tree!

Looking at it with a fresh (ish!) pair of eyes, I used the definition of bulk modulus for K. Re-arranging to give me dP = -V (K/dV) where dP is delta P (change in pressure), dV is delta V (change in volume), V is initial volume and K is the Bulk Modulus. It is then just simply a case of entering the known values on the right hand side to calculate the resulting change in pressure. Why I couldn’t see this before I cannot say...

 

[MikeHalloran]

That will give you a limit, for new clean fluid introduced by vacuum filling.

Then you might want to account for a drop of water, and an air bubble.





Mike Halloran
Pembroke Pines, FL, USA

 

[BigInch]

The air bubble will screw things up drastically.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Roylance]

Looking into it in more detail, you can account for entrained air so perhaps this is what MikeHalloran means by "an air bubble".

 

[MikeHalloran]

Hydraulic fluid will pick up air, entrained or dissolved or otherwise included in diffuse manner. Additionally, not all systems are vacuum-filled or have bleeds at all the high points, so there may be discrete pockets of air.



Mike Halloran
Pembroke Pines, FL, USA