Hydraulic Pump/Motor: Can it Work as a Motor?

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Discussion Overview

The discussion revolves around the feasibility of using a hydraulic pump as a hydraulic motor, exploring the theoretical and practical implications of such a conversion. Participants share insights on the design differences and operational characteristics of hydraulic pumps and motors, as well as the efficiency considerations involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires whether a hydraulic pump can function as a hydraulic motor, expressing a preference for hydraulic systems over mechanical ones.
  • Another participant references a conceptual interchangeability between hydraulic pumps and motors, noting that most pumps cannot be backdriven and that motors are designed for pressure on both sides.
  • A participant introduces the concept of hydro-static transmission, indicating that while pump/motors can be designed, they are not inherently interchangeable.
  • Further elaboration highlights that pumps typically have specific design features, such as a larger inlet and unidirectional operation, while motors may allow for bi-directional operation and require a drain connection.
  • Efficiency considerations are discussed, with a mention that both pumps and motors can achieve up to 90% efficiency, leading to a combined efficiency of 81% when used together, contrasted with a manual gearbox's higher efficiency.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and agreement on the interchangeability of hydraulic pumps and motors, with some acknowledging the theoretical concept while others emphasize practical limitations and design differences. The discussion remains unresolved regarding the feasibility of using a pump as a motor.

Contextual Notes

Participants note limitations related to design specifications, operational pressures, and efficiency losses, which may affect the practical application of using a hydraulic pump as a motor.

1nv3n73r
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hey people. literally just joined, hehehe
my question is, can a hydraulic pump be used as a hydraulic motor. i have an idea and want to have it operating using hydraulics rather than having shafts and gearboxes to transfere to work.
any comments welcome, good or bad, but i prefere good...hehehe
 
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From Wikipedia:
Conceptually, a hydraulic motor should be interchangeable with a hydraulic pump because it performs the opposite function - similar to the way a DC electric motor is theoretically interchangeable with a DC electrical generator. However, most hydraulic pumps cannot be used as hydraulic motors because they cannot be backdriven. Also, a hydraulic motor is usually designed for working pressure at both sides of the motor.
 
Thanks Jack action.
There is information there that I didn't know about.
 
What you are describing is a hydro-static transmission. The pump and motor can each be designed to be pump/motors, but they aren't necessarily that way, as jack action said.
 
1nv3n73r said:
can a hydraulic pump be used as a hydraulic motor.
Conceptually simple, but there are many traps for the beginner. Pumps will often have a big inlet because only atmospheric pressure is available to push oil into the pump chamber, it can have a smaller outlet.

Pumps are usually designed to rotate in one particular direction. A hydraulic pump is designed to have a low and a high pressure side with seals to prevent it sucking air on the inlet side or weeping oil on the high pressure side.

A hydraulic motor may be designed for bi-directional operation. It can be operated with positive pressure on both ports. Bidirectional motors will have a third connection to drain fluid to the reservoir tank that leaks past the internal seals.

Hydraulic motors and pumps might get to 90% efficiency. A pump driving a motor will therefore have 90% * 90% = 81% efficiency. You will need to pay for that 19% inefficiency, you will also need an oil cooler to remove the 19% waste heat. A manual change gearbox will be closer to 98% efficient.
 

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