Time to build pressure 2

[bretthydra]

I am trying to find a formula to determine the time required to build pressure in a cylinder.
ie. how much time would it take build pressure of 6000 psi in a cylinder by 'dead ending' it.

 

[hydromech]

Thanks for letting us know.

Don't forget to tell us how you get on.

 

[micalbrch]

A star for you, hydromech!

bretthydra: Tell us what kind of cylinder you think about. A kind of chamber of cylindrical shape which is pressurized by something? A hydraulic cylinder with piston and piston rod?

 

[hydromech]

I couldn't help it...I just had to do it. Bretthydra was asking for it, posting like that is just asking for trouble.

The answer depends on fluid bulk modulus, volume of cylinder, fill rate and measurement accuracy. Would it be through filling the cylinder from empty or through intensification???

 

[bretthydra]

Cheers micalbrch.
OK.
Consider the attached sketch of the piston.
To reach full stroke(16mm)in 1 second, I calculate that the flow rate would have to be 0.61932 L/min.
When the rod has reached full stroke, at what rate does the pressure increase?

 

[micalbrch]

What's in the chamber on the other side of the piston. Oil, water, air? If you want to make the full stroke of 16 mm, the other side must not contain anything. Or is this chamber not completely closed?

 

[bretthydra]

It is a spring return piston.

 

[micalbrch]

Yes, I saw that. But what is on the other side of the piston in the chamber where the piston moves into?

 

[Walterke]

All calculations aside, won't the "pressure buildup time" be nearly instant? That is, assuming the cylinder is operated with fluids, and not gases.

What exactly do you need this for brett?
Is this part of a hydraulic system?

NX 7.5
Teamcenter 8

 

[bretthydra]

We assume air.

 

[bretthydra]

Walterke.
It is intended to be operated by Oil.
Time will be a factor in the final circuit design although not to the nth degree.
I was just curious to see if there is a standard formula for the time to build the pressure. If there is, and depending on the magnitude, it may be a factor to consider in the overall design.

 

[micalbrch]

My first attempt would be Boyle's law: p1 x V1 = p2 x V2. It is only for an ideal gas and only for T=const. but at least an idea.

 

[PNachtwey]

I am trying to find a formula to determine the time required to build pressure in a cylinder.

There is no simple formula but the solution can be found using differential equations and iteration. I have done it for oil but not air. The bulk modulus for air changes as a function of pressure so I would have to modify the equation a bit.

how much time would it take build pressure of 6000 psi in a cylinder by 'dead ending' it.

Do you have a >6000 psi supply of air?


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[Walterke]

If I understand this correctly:
The side of the piston with the spring will be filled with oil, put under pressure so it moves down the 16mm.
In the bottom side there is nothing but air.

Can the air escape somehow?
Or do you want to know when the air in the bottom part will reach a pressure of 6000psi?

NX 7.5
Teamcenter 8

 

[EngineerTex]

Bretthydra,

When you say air, are you talking about a standard spring-return cylinder that has a vent on it and that the air inside is not contained and is released through a breather element? i.e., is the air on the spring side vented to atmosphere?

If so, and you are pressuring the extend side of the cylinder, the answer is a few milliseconds if not less.

Engineering is not the science behind building. It is the science behind not building.