How to deal with hydraulic and pneumatic leaks

Hydraulic Supermarket logo

In a previous article I discussed the true cost of hydraulic oil leaks. In the case of oil leaks, the cost areas that need to be considered include:

  • Make-up fluid;
  • Clean-up;
  • Disposal;
  • Contaminant ingress; and
  • Safety.

But what about hydraulics' fluid power cousin - pneumatics? One of the advantages that pneumatics has over hydraulics is its clean-ness. Air leaks are much easier to ignore than oil leaks because they don't draw attention to themselves in the same way. You don't need to worry yourself with clean-up and disposal costs. Contaminant ingression is possible, but is generally not a major concern. And unless the leak is significant, safety is not usually a big issue either. So that leaves make-up fluid (air).

Make-up air

While air is free - clean, dry compressed air is not. In considering the cost of make-up air for a pneumatics system the following need to be considered:

  • Depreciation (wear and tear) of the compressor;
  • Conditioning costs - filtration, drying and lubrication; and
  • Energy cost of compression.

The ideal leakage rate is of course zero, but when calculating the free air delivery (FAD) required by a pneumatic system a rule of thumb is to allow for leakage of 10% of total flow rate. Consider a 10 cubic meter/minute system leaking one cubic meter/minute. The power required to compress one cubic meter (35.3 cubic feet) of air per minute to a pressure of 6 bar (90 PSI) is approximately 5.2 kW. At an electricity cost of $0.10/kWh this leakage is costing over 50 cents per hour in electricity consumption alone. In a 24/7/365 operation that amounts to $4500 per year!

Quantifying losses

While a leakage rate of 10% of flow rate may sound high and would be unsustainable in a hydraulic system, air leakage rates as high as 25% are not unheard of - even in apparently well maintained pneumatic systems. The actual leakage rate of a system can be calculated using the following formula:

QL = QC* t / (T+t)

Where:
QL = System leakage rate (cubic meters/minute)
QC = Compressor FAD (cubic meters/minute)
T = Leakage time - time between compressor cut-out and cut-in (minutes)
t = Charging time - time between compressor cut-in and cut-out (minutes)
Note: this formula assumes that all system consumption is suspended while the leakage test is conducted.

Conclusion

As demonstrated by the above example, the annual cost of air leaks in pneumatic systems can be significant - in power consumption alone. Conduct regular leakage tests on your pneumatic systems and take necessary action to locate and rectify leaks as required. For more on the operation and maintenance of compressed air systems and pneumatic equipment visit: www.IndustrialPneumaticControl.com

Related articles:

Hydraulic maintenance lessons from the Qantas mid-air emergency
Hydraulic cylinder failure caused by the 'diesel effect'
How to deal with air contamination of hydraulic oil

If you enjoyed this article, you'll love Brendan Casey's Inside Hydraulics newsletter. It gives you real-life, how-to-do-it, nuts-and-bolts, hydraulics know-how -- information you can use today. Here's what a few members have said about it:

Can't Put It Down
“I get e-mails like this all the time. I never find time to read them. I decided to read Issue #30 and I couldn't put it down. I'll make time from now on.”

Richard A. Shade, CFPS, Project Engineer (Hydraulic Design), JLG Industries Inc.

So Valuable It Earned Me A Raise
“The knowledge I've gained from this newsletter has been so valuable it has earned me a raise!”

Jack Bergstrom, Heavy Equipment Mechanic, Sharpe Equipment Inc.

Love It - Keep Them Coming
“I just love this newsletter. As a Hydraulics Instructor for Eaton, I make copies and distribute them to my students as I address various topics. Please keep 'em coming.”

Michael S Lawrence, Hydraulics Instructor, Eaton Hydraulics Inc.

To get your FREE subscription ($149 value), simply type your first name and primary email address into the form below and hit 'SUBSCRIBE NOW!'

First Name *
Email *

This is a private mailing list that will NEVER be shared for any reason.
You can also unsubscribe at anytime.

Home Page



Copyright © 2000 - 2013 Brendan Casey; HydraulicSupermarket.com