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Hydraulics 101

Sunday, June 1, 2008

With the increased number of questions and comments­ I decided to talk about your sweeper/scrubbers hydraulic systems. We’re going to discuss not only the problems and solutions but some of the causes as well. Let’s begin, first, by talking about a planned maintenance program everyone should follow. With such a plan, many of the problems we will talk about simply will never take place.

Maintenance Charts change from one machine manufacturer to the other, but not by much. There are basic fundamental service areas that I have listed for you to study. I am listing these by frequency, but make no mistake; all are equal in importance.

#1 — Check hydraulic reservoir gauge and fill as needed.

#2 — Check the function of the directional control pedal and adjust if required. This helps so the machine does not creep forward or backward.

Every 50 hours:
Inspect the hydraulic oil cooler and clean with air, if needed.

Every 500 hours
#1 — Replace the hydraulic breather cap filter on top of the hydraulic tank.

#2 — Replace the hydraulic fluid and the filter.

#3 — Clean or replace the hydraulic fluid strainer inside the tank reservoir.

With a sweeper/scrubber there are many hydraulic motors. You have the main brush motor and side brush motor usually three scrub brush motors, not including the wheel/drive motor. So you can see motor failure is very common. And what is the cause of motor failure? Usually worn parts such as o/Rings or seals caused by ware, heat or a build-up of dirt or grit in the line. Once dirt is introduced, then the shaft gets grooves cut into them. Once you know it, a motor fails. If caught early enough a seal kit usually solves the problem. Another tell-tail sign is a leaky motor. A leaky motor again usually just requires a seal kit.

When you have a bad wheel/drive motor it is usually serious. If your lucky the shaft seal will break down and leak. In most cases you can get by with just a seal kit. However, if the motor is not leaking and making a tremendous amount of noise, I am afraid it’s going to be bad news. The gears are going to be worn or scored with grooves.

The inside of the pump will be worn beyond repair which means new pump. Yes, so what causes such a thing to the hopper.

#1 — It could be a stuck relief valve

#2 — It could be a low level of hydraulic fluid.

#3 — Perhaps a clogged hydraulic oil strainer

#4 — Foreign material such as dirt was introduced into the system over the life of the machine.

I have always encouraged stocking the seal kits of the hydraulic motors. If you can catch these problems in time, usually a kit takes care of any problems and can save a lot of money for new hydraulic components.

Lastly, the most common complaint to me in the hydraulic system is noise. Here is what I’ve found in most cases:

#1 Cause of Noise — Low hydraulic fluid. Usually when I tell them to check the level, it’s low. Fill the system, the hydraulic noise disappeared.

#2 — Clogged suction or in-line hydraulic filter

#3 — Internal Pump or motor damage

#4 — Relief valve stuck or dirty.

#5 — loose suction line.

So, I say to you, did you check your fluid today?

Also, here is what I have on Hydraulic Fluid Specifications
SUS @ 100 degrees F 510-560
SUS @ 210 degrees F 78-84

As always, thank you for reading. You can e-mail me at with any questions or comments.

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