Hydraulic motor case flushing

Hydraulic motor case flushing

Hydraulic motor case temperature

At the latest my project I used hydraulic motor Rexroth A2FLM710 (710cc). The motor works at 1400 rpm and provides 590 HP to the consumer. Foe safe motor work I always try to keep the case temperature below 80*C. The easiest way to do this is a flushing flow adjustment.

In addition to the flow, you need to keep eyes on a case pressure and try balancing to prevent overpressure in the motor case (check in the motor manufacturer’s catalog the max available case pressure to make longer life of motor shaft seals).

The values I came are 21 GPM at 30 psi case pressure and in the worst-case scenario (max motor load, warmed hydraulic oil) case max temperature was around 80*C

Hydraulic motor case flushing

Hydraulic motor case flushing flow and case pressure

There no prescriptions or recomendations for valve or orifice size in motor catalogs for flushing flow, so the selection of flushing valves is a challenge.

Of course, you can find orifices (with different diameters) provided by the manufacturer with the motor in the motor’s catalog. But the flow and result case temperature will be different from application to application and the selection of correct orifice is an engineering responsibility without any help or advice from motor manufacturer.

Moreover, the manufacturer can’t provide all range of orifice diameters so the selection in the catalog is usually limited. And as you can see, sometimes values of flushing flow can be really huge and the only experience helps me to select the right flushing valve size at the beginning of the project.

I still believe, manufacturers can provide some diagrams/charts with correlation power-> flushing flow for approximate/preliminary estimation of the flushing valve size. Because I do not think everyone has a chance to make long tests during production and play with valves sizes…

What do you think?


  1. Armando H

    Hello, check the table in the training 4 by Rexroth, pg 61, I will send you by email,
    regards from Mexico,

    1. Dzyanis (Post author)

      Hello Armando. Thanks for your post. The photo of the book page you sent me by email is an orifice size selection at the pressure-flow chart like I have already posted in the article https://fluidpower.pro/orifice-flow-calculation/. With this chart, you can select propper orifice to get the required flow at a known pressure. The problem I try to illuminate in the post above is different. The problem is in a preliminary determination of required case flushing flow (using a motor size and a power provided by the motor to the consumer) to prevent overheating the motor. As soon as you know at least approximate value of required flow you can play with orifices (or flow control, or pressure flushing valves) to find the best size – using the chart you provided.
      I can’t find the way how to calculate the required flushing flow at the beginning of the new project to get the theoretical value of max safe motor case temperature. But I’m sure, manufacturers can provide some charts to help engineers to find a required flow as a start point.


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