Piston Pump Case Drain Temperature

[NJAus1]

Hi All,

I wanted to understand how a piston pump that wears over time results in an increase in case drain temperature. With age the case drain flow increases which I understand.

I have had an explanation: Case-drain flow does no useful work and is converted into heat. I don't quite understand thr above statement.

Could someone explain the temperature increase simplistically?

Thanks in advance.

 

[1503-44]

Energy expended by the pump that does not result in moving fluid and increasing the pressure, "the useful work", results in heating of the fluid and the pump itself. If your pump is operating at 75% efficiency, then 75% of its energy is doing useful work and 100%-75% = 25% of its energy consumption is heating things up.

 

[LittleInch]

The case drain fluid is fluid leaking passed (past?) the cylinder seals. It does this more when at high pressure, so that high pressure fluid suddenly becomes low pressure fluid in the casing sump and that energy is converted to heat.

So it's a bit of an odd explanation, but is correct, i.e. the fluid is being pressurised, but the flow is going into the casing and not the discharge and hence doing no useful work.

The more fluid, the hotter the casing gets as it all heats up.

Does that make more sense?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hydtools]

The case drain carries the leakage flow away from the pump Leakage occurs between pump pistons and their bores, between the slippers/shoes and plate, between pump pistons and piston shoes. Wear results in more leakage and more power not doing useful work equals more heat generated appearing in the case drain.
In a gear pump wear allows more leakage between the gears and housing.

Ted

 

[TugboatEng]

An alternative way to think is that there is heat from friction generated as the fluid slips between the piston and cylinder.

I don't agree with the no work done statement. The work is done while squeezing through the clearances.

 

[LittleInch]

No "useful" work is what was said.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

The OP is asking about how the heat ended up in the case drain. There are other useless works done that may end up being lost through the discharge, lube, etc but this is fluid that has had work done on it and it's pressure has been increased and it is moving past the pistons.

 

[1503-44]

Nobody said that work was not done on the case drain fluid. Energy was expended and work was done on the case drain fluid, but that resulted only in a temperature increase. Its just that a temperature increase alone is not considered as "useful" work.

 

[hydtools]

If you intend to raise the temperature, it is useful work. If you did not intend to raise the temperature, it is not useful work = wasted energy.

Ted

 

[1503-44]

Take that argument to wiki.

https://en.m.wikipedia.org/wiki/Work_(thermodynamics)[/URL]]
Work, i.e. "weight lifted through a height", was originally defined in 1824 by Sadi Carnot in his famous paper Reflections on the Motive Power of Fire, where he used the term motive power for work. Specifically, according to Carnot:

We use here motive power to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it is raised.

 

[NJAus1]

I get the concept that heat is generated but if heat is the transfer of thermal energy, then what is transferring the heat.

 

[1503-44]

Heat is not exactly the transfer of thermal energy. Heat is often, but not always, realised by the accumulation of energy by an object, it is usually, but not always, manifested by an increase of its temperature. Radioactive decay can bring about heat without transfer.

https://www.britannica.com/science/heat[/URL]]Heat, energy that is transferred from one body to another as the result of a difference in temperature. If two bodies at different temperatures are brought together, energy is transferred—i.e., heat flows—from the hotter body to the colder. The effect of this transfer of energy usually, but not always, is an increase in the temperature of the colder body and a decrease in the temperature of the hotter body.

The oil and other parts of the pump are accumulating energy not usefully consumed by the pump in transformation of that energy into mechanical work taking place within the system and, as a result, its temperature is increasing.

 

[NJAus1]

As the fluid on the case drain increases in temperature then heat needs to be transferred, the pump is generating heat from it inefficiencies that cause the fluid in the case drain to increase?

If I treat the case drain as a closed system, then there is no useful work being done by the system, the pump is transferring heat to the system which increases its internal energy and thus the temperature?

 

[1503-44]

Correct.
Correct.