Prelube FAQ

What you need to know about prelube.

Why Prelube?
What size pipes should I use?
Where is the best place to plumb in the prelube pressure line?
Where is the best place to connect the prelube suction line?
How do I run the power to the prelube pump?


Why Prelube?

It is widely understood that the period of time between when the engine begins to turn at startup and the time when fresh oil from the sump reaches moving parts causes the vast majority of the wear an engine sees during its lifetime. A prelube pump puts the oil where it is needed before the engine begins to move, thus reducing this high wear period.

Click the image to take a closer look at how Prelube works.
PrelubeAnimation400 (50K)

Historically operators of large engines would avoid shutting them down. This was done to reduce startup engine wear in addition to other operational advantages. The largest engines might only be shut down every few months for periodic maintenance. Fuel was inexpensive and environmental concerns were not considered. As the price of fuel climbs ever higher and idle emissions are no longer acceptable, operators are shutting down engines more than ever before.

Fuel costs as well as the EPA and other regulatory agencies are increasingly restricting engine idle time. As a result the number of times some engines need to be started in their lifetime may go up from as few as 80 or 100 to as many as 86,000 times. It's easy to see how wear rates that were considered acceptable with only 80 lifetime starts would have a significant impact on engine life with 86,000 lifetime starts.

In the end the decision as to whether a prelube system is appropriate for a given installation comes down to the cost benefit analysis of three factors. The number of times the engine will need to be started in its lifetime, and the cost of replacing/rebuilding the engine (including equipment downtime), against the cost of adding the prelube system.

As an example, a good prelube system may run in the range of $1500 by the time it is installed. So if the engine is small and only costs $10,000 a prelube may be impractical. As the engine size goes up in the calculation though, a $1500 investment could save many times its price in future repairs and downtime. Likewise if an engine were only going to be shut down every three months for maintenance, the cost of a prelube system might be unjustified but for a system that is restarted multiple times a day it would be a necessity.

Click the icon to download a Spreadsheet to help you calculate the prelube savings for your application. Or Scan the QR code with your android phone to use our calculator application.

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What size pipes should I use?

There is no short answer to this question, but if there were it would be as big as possible.

The pump itself does not create pressure. It produces flow. Like a turnstile, every rotation of the pump delivers a metered volume of oil to the other side. Whatever system is connected to the pump has flow resistance that produces backpressure as the pump motor works to maintain flow.

Available pump motor horsepower can develop only a given amount of pressure. Each elbow and each inch of pipe has a cumulative effect. If the plumbing uses up all available pressure there will be no pressure left for the job the pump is intended to do.

Because these oil pumps can not run at thousands of psi like a hydraulic system, excessive pressure drop caused by small pipes can be detrimental to system performance. Small suction pipes will starve the pump and reduce output flow by causing cavitation. Small pressure pipes will create excessive backpressure that will reduce output flow by slowing down the pump motor. Therefore, elbows and long runs of pipe should be avoided.

NOTE: The suction side of the pump is especially vulnerable to restriction. Pipes should be as short and large as possible. Cold oil is like honey. If you were going to try and suck honey thru a straw you would need to use the biggest straw you could find.

Varna Pumps have ports sized for the pumps deigned flow. In almost all cases smaller pipes should not be used. If for instance a smaller fitting in the oil pan is all that is available port-sized hose should be used up to that point and then reduced, rather than reducing at the pump and running a smaller line.

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Where is the best place to plumb in the prelube pressure line?

This can be one of the biggest challenges to adding a prelube system to an existing engine if the engine was not designed for it.

Even among engines of the same model there is a tremendous amount of variation from engine to engine. It is therefore more practical for us to address each installation on its own. We are always happy to help. Give us a call for engineering assistance and support.

In general the best place is between the service oil pump and the filter, often at the oil filter housing it's self. Some engines have a port in the block that can be used. The point where the oil enters the engines oil galleys should be as far as possible from the oil pressure sending unit as possible so that when oil pressure is shown on the gage it is sure that the engine has oil all the way through its oil galleys.

Prelube oil should be filtered. This can be done ether by connecting the input line between the service oil pump and the filter or by using a dedicated inline filter for the prelube system.

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Where is the best place to connect the prelube suction line?

Again even among engines of the same model there is a great deal of variation from engine to engine. It is therefore more practical for us to address each installation on its own. We are always happy to help. Give us a call for engineering assistance and support.

In general the oil needs to come from the oilpan and so the suction line needs to connect there. Many engines have a threaded fitting available already. If there is an access plate it can be removed and a threaded hole machined in it. Some pans may need to be removed so that an appropriate bung can be welded or machined in. If the connection is on the side of the pan a pickup pipe may be needed inside and so the connection should be made in-line with one of the main bearings so that the pickup pipe will not interfere with the crack shaft.

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How do I run the power to the prelube pump?

In most cases an electrical motor is used to run the prelube pump (though air motors are available). Wire size should be based on the motor nameplate amps and an appropriate breaker or fuse should always be used.

The simplest wiring setup would be a push-to-close switch running a relay that delivers the power to the pump. With this system the operator simply holds the switch until oil pressure begins to show on the gauge. Some Engines have a "glow plug" output that can be used to trigger the prelube cycle and more sophisticated engine controllers have a dedicated Prelube control circuit. For more detailed information of controls circuits see our prelube control circuit page. We are available for engineering assistance here as well. Let us know what you would like to do and we can help you set up your control.

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Direct shaft couplings used in most Varna pumps eliminate the cost, bulk and limited life associated with traditional 'soft' couplings. While it takes careful design and precision manufacturing methods to get this to work, it produces a superior pump in all respects.


Customer Feedback "I am in love with these pumps. The best feature is that I can dead head the pump and there is no screaming PRV."
Wes Blankenship of Symbrium, Inc.


Article Link
Considerations in wiring power to a prelube pump


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