PISTON AXIAL MOTORS

a. Make sure your fluid is clean, and of the right type/temp.

b. check with the manufacturer

c. if its too thin, you will have less than suitable lubrication, and cause catastrophic failure, Too thick and you can also have catastrophic failure. CHECK WITH MANUFACTURER. use the recomended oil as per your pump/motor manufacturer. I cannot stress this enough. You MUST follow recomendations set by the manufacturer to avoid failure.

Temperature should be monitered to maintain the correct viscosity, and keep the oil CLEAN.

When you tear a pump/motor apart, you can determine operating conditions depending upon the type and location of wear on the internal components. Consult your manufacturer, and find a proper hydraulics service center.

Have you read the book you received for the class? If the answers to the test questons are not in there then the instructor should have given them during class time. Probably the one you skipped.

Dear ATIF NAVEED,

AXIAL - PISTON MOTORS use the reciprocating piston motion principle to rotate the

output shaft,but motion is axial rather than radial. Please remember that these motors

have excellent high speed capabilities, but unlike radial piston motors,they are limited at Low Operating Speeds. The inline type will operate smoothly down to 100 rpm & the bent axis type to 4 rpm range.

SELECTION OF HYDRAULIC MOTOR - the application of the hydraulic motor dictates the required HORSEPOWER & MOTOR SPEED RANGE. the type of motor selected depends on the reliability, life, and performance.

HYDRAULIC OIL - Hydraulic oil can be one of the most vital components of the hydraulic system.So you must carefully consider not only the viscosity but also the following characteristics :

* Thermal stability

* Hydrolytic stability

* LOw chemical corrosiveness

* High anti-wear properties

* Low tentency to cavitate

* Long Life

* Total water rejection

* constant VISCOSITY regardless of Temperature

* Low cost

NO SINGLE OIL HAS ALL THESE IDEAL PROPERTIES. Therefore it is possible to select one that is the best compromise for a particular Hydraulic System.This selection requires knowledge of the system in which the oil is used.

My suggestion is simply to follow the manufacturer's advice because they would have

considered the following parameters:

* Max. & min. operating temperatures

* Type of Pump

* operating Pressure

* Operating Cycle

* Loads acting on various parts

* Type of control & power valves

HYDRAULIC MOTOR MALFUCTIONS - The majority of motor problems fall into the following 3 categories:

1. IMPROPER OIL -It must have CLEAN oil, in adequate supply, and of the proper Quality & Viscosity.

2. POOR MAINTENANCE - A poor maintenance program runs a close second in the cause of major problems.

* failure to check & repair leaking lines & connectors

* Failure to install motor correctly

* Failure to find the motor malfuction

3. IMPROPER OPERATION - Exceeding the motor's operating Limits. Excessive Torque/ Load can create Bearing & Shaft fatigue. Excessive Temperature can cause loss of efficiency because the oil becomes thinner & can produce rapid wear due to lack of Lubrication.

You may visit www.hydraulicspneumatics.com for further fluid Power Reference Materials & standards.

Hope you will find the above data useful.

Kind Regards

P.Rangasamy.

Hi,

pistons have two bearing surfaces, both should act as hydrodynamic bearings, but this needs a minimum velocity times viscosity.

So at low speed a higher (than recommended) viscosity would be better.

At high speed there is a lot of hydrodynamic loss, so low viscosity would be better.

As the loss is heating the oil and thus lowering viscosity this effect should stabilise the situation to some extent.

As stated in previous posts the most severe damage can be done by particles: these scratch the surfaces as being bigger than the hydrodynamic film thickness.

Scratched surfaces will no longer have a full hydrodynamic action but some metal to metal friction, thus severely or catastrophically limiting lifetime.

I have a possibility to measure hydrodynamic film thickness but this is requiring electrical isolation of the output shaft to housing. And this is expensive (20K$ and more depending on modification necessities). This was originally developed to measure lubricant films in ball bearings but was used also in hydrodynamic lubrication.

RHABE