Flow Loss In A Gear Pump

• Worn teeth profile on the gears
• Worn seals
• Worn seats
• Slipping couplings
• High torque at the motor
• Partially blocked delivery pipe
• Leaking delivery pipe
• Partially blocked inlet pipe
• 2-phase flow
• Spill-back valve pressure set too low

. . . and low speed. Motor failing?

what is the enviroment temp. there.

It's the result of the pumps design. Gear mesh, tooth wear, housing wear all deteriorate as the pump runs. Since all these wear points open bypass flow paths a gear on gear pump will constantly lose efficiency as it runs.

If possible change to a Vane pump that has wear compensation built in to the design and holds its efficiency until it falls apart.

Over the years I have replaced many Gear pumps with vane pumps and made slow over heated circuts operate like new for long periods.

One thing that is required is clean oil. However, that makes any pump design last longer, even Gear designs.

If two stage pump, bad bypass valve.

Dirty filter strainer on the suction line

Worn pump

Bad pressure relief valve

The major problem is that at the start of the pump,the pump flow will maintain a contant flow of 25GPM after about two hours or more the the flow will start falling to 17GPM making panel indicating low oil flow to the Vertical Raw mill of the cement plant.

Good Morning Olusola,

your observation clearly is referring to influence of viscosity (oil/fluid temperature): for the cool oil the clearances inside the gear pump do not allow as much pump-internal leak flow than for the warmed-up (thinner) oil.

The volumetric efficiency of a gear pump in principle is working like this but if your fluid is not of extreme low viscosity (means, if it is common hydraulic oil for lubrication) the effect should be very, very small - typical vol.efficiency in range of ETA_Vol = 0.95 or better.

In raw mill environments a lot of dust from milling process becomes accumulated. Those materials are very fine and will enter any cavity and machines clearances. This way it is entering the fluid as well. In fact oil filters normally are installed in the pressure line ("behind the pump") particles carried with the fluid are passing the pump. This way the pump components easily can become subject to serious wear and it may cause you to get the pump replaced after a couple of month already.

Common gear pumps housings are made from Alu-alloy. They are pricy - but reliability in dirty environments is doubtful. For better money you can get gear pumps with housings from cast iron. You may also ask you hydraulic supplier to have a look for a pump which is able to operate on wider internal clearances (e.g. as they are used for emulsified fluids). Those pumps are expensive but their volumetric efficiency is more stable.

As an alternative you may add a bypass circuit to the main fluid tank. This circuit is overtaking a basic filtration of the fluid. It is useful to have the oil tank divided in 2 or 3 sections, which are in contact through defined ports.

The first chamber used for inlet of the used oil (air release, calming down the flow dynamics and foaming). From that chamber the oil is flooding the second chamber through a port in bottom position.
At second chamber the oil filtration circuit will take the oil and press it through a fine and large filter (e.g. 25 micrometer mesh or better). The discharge from filtration circuit is filling the third chamber with cleaned oil. From third chamber the regular lubrication pump is taking the oil.
between second and third chamber a small port in high position should be considered, to allow a uniform filling level and ensuring propper filling of third chamber in case the filtration circuit would break down.

Hope, this gives you some ideas

Ceeping the oil clean is the best measure for reliable and trouble-free equipment!

Albert

Have you checked the type of oil in your hydraulic plant? Wrong viscosity or aged oil would give result as described when the oil temperature is rising.

PWSlack is pointing to most of the factors that can affect the oil flow in a gear pump.

Previous contributors have mentioned your oil may be worn and /or contaminated. If you have a large volume of oil in this system (significant cost) you can have it tested. Lubricant distributors can do this or tell you who can test it. This can tell you if you need to change oil. Moisture content could cause a viscosity decrease with temperature. Of coarse if its contaminated, damage has probably already been done.

Use filters as low as 5 micrometers you encrease life by a high factor.

Use as it was already said a second pump to filter oil and as well inlet as outlet filters.

The cost of filters is peanuts in comparison with cost of maintenance and spare parts.

Check also the cooling of oil. If underdimensionned the higher the temperature the higher the losses and the wear.

How long had the motor been in use! Perhaps wrongly sized?