How to determine cylinder pressure?

[Michael.Bull]

• I am calculating the velocity at the orifice of a pneumatic cylinder using Bernoulli's equation.
• I need help determining the pressure inside the cylinder (P1).
• The pressure inside the cylinder is not simply F/A due to the presence of the orifice.
• When applying Bernoulli's equation, I assumed:
  • The highlighted term in the equation can be neglected. - I'll likely redo the calculation to include the term.

Please help determine the pressure inside the cylinder.

 

[3DDave]

The pressure in the cylinder will be the stagnation pressure of the flow. This flow is unlikely to last long as far as putting fluid into the cylinder.

What is the circumstance where this would matter?

 

[Michael.Bull]

The pressure in the cylinder will be the stagnation pressure of the flow. This flow is unlikely to last long as far as putting fluid into the cylinder.

What is the circumstance where this would matter?

I have an object that is spring loaded. If someone lets go of the object it will spring back quickly, potentially hurting someone.
I want to dampen how quickly the object springs back.

 

[3DDave]

They make needle valves with very tiny amounts of section area to make sure the flow out of the cylinder is very small.

As an example - I had a screen door damper that had become unreliable. I drilled a hole with the smallest bit I have - about 0.003 inch diameter. This provided enough flow out of the cylinder with the force of the internal spring as to act as if there was no restriction at all.

Consider getting a shock-absorbing cylinder that uses oil as the working fluid with a properly sized orifice for control.

 

[Snickster]

Here is link that has discussion about flow through orifices. Follow the equations but modify those equations based on the following:

The pressure inside the cylinder P1 is the applied force F divided by area of the piston A1 = F/A1.

The initial velocity V1 in the cylinder is zero.

P2 term and those with "h" height difference are zero as you already show.

Orifice, Nozzle and Venturi Flow Rate Meters

The orifice, nozzle and venturi flow rate meters makes the use of the Bernoulli Equation to calculate fluid flow rate using pressure difference through obstructions in the flow.

www.engineeringtoolbox.com

 

[Doug Hunter]

• I am calculating the velocity at the orifice of a pneumatic cylinder using Bernoulli's equation.
• I need help determining the pressure inside the cylinder (P1).
• The pressure inside the cylinder is not simply F/A due to the presence of the orifice.
• When applying Bernoulli's equation, I assumed:
  • The highlighted term in the equation can be neglected. - I'll likely redo the calculation to include the term.

Please help determine the pressure inside the cylinder.

I think to properly analyze, we need a better understanding of your boundary conditions and causality. Maybe it's just me not seeing it, but is the flow being pushed into the cylinder to push the rod, or is the rod being pushed in to push the flow out?