# Help with formulas for calculating pressure

Hi! This is my first post on here. I need to purchase an air cylinder, most likely hydraulic. The cylinder will have a forming die attached on the end and will be used to crimp two small stainless steel tubes together. The crimp will occur at an offset of .004 inches from each end of the tubes. They are thin tubes, as the ratio of the inner diameter and the thickness are less than 20. How can I calculate the pressure required to execute this task? Is there a specific set of formulas? Any help is greatly appreciated.

## Answers and Replies

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berkeman
Mentor
Welcome to the PF.
I need to purchase an air cylinder, most likely hydraulic.
"Hydraulic" implies a fluid medium, "pneumatic" would be more consistent with "air cylinder". Which one do you want to use and why?

Can you post links to similar presses that you have looked at? Thanks.

jrmichler
Mentor
A cylinder develops force equal to the pressure that is applied multiplied by the area of the piston. The piston diameter is the nominal cylinder size, that is a 100 mm cylinder has a piston 100 mm diameter. Typical compressed air systems are at about 100 PSI. Typical hydraulic systems run at 1000 to 2000 PSI. The rated pressure of the cylinder is the maximum pressure that you can put to it. You need to make sure that the pressure applied to the cylinder is less than the cylinder rated pressure.

Read some cylinder catalogs. Pay special attention to the parts about buckling when using a cylinder to push on something.

There are no easy to use formulas to calculate the force needed to crimp tubes. You just increase the force until you get repeatable, reliable crimps.

jim hardy, russ_watters, Asymptotic and 1 other person
A cylinder develops force equal to the pressure that is applied multiplied by the area of the piston. The piston diameter is the nominal cylinder size, that is a 100 mm cylinder has a piston 100 mm diameter. Typical compressed air systems are at about 100 PSI. Typical hydraulic systems run at 1000 to 2000 PSI. The rated pressure of the cylinder is the maximum pressure that you can put to it. You need to make sure that the pressure applied to the cylinder is less than the cylinder rated pressure.

Read some cylinder catalogs. Pay special attention to the parts about buckling when using a cylinder to push on something.

There are no easy to use formulas to calculate the force needed to crimp tubes. You just increase the force until you get repeatable, reliable crimps.
Do you have an idea of a suitable psi range ?

jrmichler
Mentor
Parker is a well known brand of pneumatic products. Their heavy duty air cylinder catalog has a good section on how to buy and install air cylinders: https://www.parker.com/literature/Industrial Cylinder/HY08-0910-1NA.pdf. Pages 44 through 57.

Every compressed air system needs pressure gauges near where the air is used. Like these: https://www.omega.com/pptst/PGC.html. Even a simple system with a Home Depot air compressor connected to one air cylinder. First you find at what pressure your system is operating, then you specify a cylinder to work at that pressure. Pressure gauges are cheap. Don't be afraid to buy a few.

jim hardy, Asymptotic and russ_watters
jim hardy
Gold Member
2019 Award
Dearly Missed
Just a thought here........

Pay attention to the mechanical layout of your press.
If something can slip loose and let the cylinder extend fully ,
make sure it can't crush somebody's hand along its way .

The energy stored in compressed air behind a piston can launch parts flying
whereas hydraulic oil, being incompressible, will move the piston only a few mils should your die fail.

I like inherently safe design.
Let Mother Nature help you toward that end....

Compressed air and compressed springs that get loose are deadly .

old jim

jrmichler
ChemAir
Gold Member
Parker has a product for crimping copper tubes for refrigeration systems. It may be of interest to look at the tool they use. I believe it will operate off of a 16V Makita rechargeable battery used on hardware store drills/impacts/etc. According to their literature, for copper up to 1-1/8" (type ACR, L, or K), the tool provides a crimping force of 19 kN. The crimp that will go up to 1-3/8" is 24 kN. Maybe these values will give you some order-of magnitude help if your crimp is a clamshell style..

https://www.parker.com/literature/Aftermarket AC and Refrigeration Division/Misc. docs/Literature PDFs/Catalog K-1 ZoomLock.pdf