Fluid Power Journal

Problem: Highest Pressure

Cylinders are 2″ x 10″ x 1″    •      Supply Pressure is 100 PSI

Question:  What is the highest pressure that the gages A & B will see without any shock loading or any inefficiency?

A:___?____        B:___?___    

Find Out The Solution

Have you heard of the saying, “When in doubt, meter out”? Be careful. These two problems are a bit tricky, and most individuals don’t realize or even think about the intensification of pressure when using a meter-out circuit.
Problem A:Calculate total force to extend piston: F = PA & A = D² x 0.7854

A = 2² x 0.7854 = 3.14 in²; Using F = PA F = 100 x 3.14 or 314 lb.

Now subtract the 250-pound mechanical load from 314-pound pneumatic capability = 314 – 250 = 64 lb.

This remaining load is held back with the rod end area of the cylinder. Effective rod end area (EREA) = 3.14- 0.7854 = 2.36 in²

Using F= PA 64 / 2.36 = 27 psi on extension

Note: On retraction, the gauge will go to 100 psi when the cylinder is fully retracted.

Answers for A: 27 psi on extension and 100 psi on retraction

Problem B:

Here we have an intensification problem. The extending force from the mechanical load is 250 lb. The extending force from the air pressure is again 314 lb. Together that is 564 lb pulling down supported by the EREA of 2.36 in² (F=PA) or 239 psi. That is 564 / 2.36 = 239. On retraction, the gauge read about 80 psi without inefficiency until fully retracted and then read 100-psi system pressure.

Answer of B: 239 psi on extension and 100 psi on retraction.

Note: It would actually take about 106+ psi to lift the load, but system pressure is only 100 psi.

Best answers are 100 psi for A and 239 psi for B.

This is why manufacturers design and rate their valves higher than normal system pressure.

Deadline past. Not available for submissions.

Winner:

Ronald Arreola, CFPS, Hydraforce, Inc., Lincolnshire, IL

Answered Correctly:

Harold Lawson, CFPPS, Air, Inc., Franklin, MA

John Guerrant, CFPS, Charlotte, NC

David Thun, Chanhassen, MN

By Ernie Parker, AI, AJPP, AJPPCC, S, MT, MM, MIH, MIP, MMH,
Fluid Power Instructor, Hennepin Technical College, EParker@Hennepintech.edu

This teaser is printed in the Fluid Power Journal. Submit your answer HERE. Those who submit the correct answer before the deadline will have their names printed in the Society Page newsletter and in Fluid Power Journal. The winners will also be entered into a drawing for a special gift.

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