Troubleshooting hydraulic failures

A White Drive Products product story

Edited by the Engineeringtalk editorial team Jan 11, 2005

Applications engineer Dick Zachery offers tips for troubleshooting hydraulic motors for attachments.

It's a dark and snowy winter morning.

Eighteen inches of wet and heavy snow fell overnight.

Jake arrives at his first ploughing job with his skid steer loader and snow blower attachment.

Jake attempts to start the blower and to his amazement the blower isn't turning.

Soon his screams of shock, disappointment and horror can be heard echoing throughout the quiet suburban streets.

Jake encountered a corollary to Murphy's Law: Whatever goes wrong happens at the worst possible time.

The big question is, what do you do next? Troubleshoot.

But, where does Jake begin?.

For hydraulically driven attachments, troubleshooting is a process that's pretty much the same for nearly all attachments - whether it's a snow blower, mower, stump grinder or auger.

So there are four main areas to investigate: the hydraulic power unit; the hose and piping; the motor; and the motor and attachment connection.

Step 1: make sure quick disconnects are secure and in proper rotation position.

Then check for failed motor/attachment connections and review all the hydraulic piping and hoses for collapses and holes that could cause leaks or restrictions.

Step 2: make sure the hydraulic power unit (HPU) is generating hydraulic power by making certain the filters (filler breather, oil intake and return) are not clogged or dirty.

Step 3: attach a flow meter/pressure gauge combination on the outlet side of the HPU to ensure the proper amount of flow and pressure is being generated.

Step 4: place the flow meter on the return side of the motor to determine if the proper amount of flow is being created across the motor.

If proper flow exists but the motor is not turning, then it is a motor failure.

By following this process, Jake's screams of horror turned into frozen tears of joy when he found out the quick disconnects weren't fully engaged and secure.

All's well that ends well.

There are a number of potential hydraulic motor problems and causes, of which the first to consider is cavitation.

Cavitation, or introduction of air, is manifested with a noisy, chattering sound and can cause rapid motor and pump failure.

Check for low oil, over-running load, loose connections, a dirty breather or filters, or thick/cold oil.

The second is an overrunning load.

Here, the motor is attempting to be stopped with a four-way, three-position, closed-centre (all ports blocked) valve, but the attachment inertia continues to drive the motor turning it into a pump.

This can lead to cavitation and overtorquing of the motor.

The third problem is overspeeding of the motor.

Tractor and skid steer manufacturers continue to increase the capacities of their hydraulic systems.

For many end users, faster is not always better.

Excessive flow to a motor and the resultant overspeed condition can cause excessive system temperature and motor failure due to breakdown of the oil film.

Motor failure will result in weak performance or complete lockup.

Beware an overtorqued motor.

Excessive pressure and pressure spikes can overload the motor drive components, resulting in broken drive links, broken output shafts or failed bearings.

Check relief valve settings, coupling alignment and sprocket/pulley diameters that may be causing excessive radial load.

Failed connections are a frequent problem.

Check key stock or pin stock material and ensure there is a snug fit.

Check for broken/slipping belts and check set screws.

Restrictions in lines are commonplace.

Check for a collapsed hose, clogged filter, hose sized too small or orifice or fitting restrictions.

Contamination can be a problem.

Check for condensation (a milky appearance of fluid), dirt and thermal breakdown, which looks like dark, burned fluid.

Heat is also an issue.

High system temperature can lead to poor performance and premature failure.

This can be caused by thin oil, extended duty cycles, a reservoir low on oil, oil bypassing through the relief valve or an undersized cooler.

Finally, look out for wrong rotation.