How to deal with bent hydraulic cylinder rods

Hydraulic Supermarket logo

In a previous article, I discussed ways to reduce the recurring cost of hydraulic cylinder repairs. And one of the topics discussed was cylinder-rod buckling loads. In response to this article, many or our readers wanted to know how to deal with bent rods in a repair situation.

Checking rod straightness

Rod straightness should always be checked when a hydraulic cylinder is being re-sealed or repaired. This is done by placing the rod on rollers and measuring the run-out with a dial gauge (Figure 1). Position the rod so that the distance between the rollers (L) is as large as possible and measure the run-out at the mid-point between the rollers (L/2).

Checking Rod Straightness

Figure 1. Checking rod straightness.

Allowable run-out

The rod should be as straight as possible, but a run-out of 0.5 millimeters per linear meter of rod is generally considered acceptable. To calculate maximum, permissible run-out (measured at L/2) use the formula:

Run-out max. (mm) = 0.5xL/1000
Where: L equals distance between rollers in millimeters.

For example, if the distance between the rollers was 1.2 meters, then the maximum, allowable run-out measured at L/2 would be given by 0.5 x 1200 / 1000 = 0.6mm.

Dealing with bent rods

In most cases, bent rods can be straightened in a press. It is sometimes possible to straighten hydraulic cylinder rods without damaging the hard-chrome plating, however if the chrome is damaged, the rod must be either re-chromed or replaced.

If a rod is bent, then it is wise to check actual rod loading against permissible rod loading based on the cylinder's mounting arrangement and the tensile strength of the rod material. The formulas and procedure for doing this are explained in detail on page 58 and 59 of Industrial Hydraulic Control. If actual road load exceeds permissible load then a new rod should be manufactured from higher tensile material and/or the rod diameter increased to prevent the rod from bending in service.

Related articles:

Straight talk about bent hydraulic cylinder rods
How to test hydraulic cylinders
How to store hydraulic cylinders - safely

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