What are the advantages of a Gerotor pump over a spur gear design?

Smooth Pumping Action - Each rotor revolves around it's own center with no inherent imbalance. Gradual change in pumping pockets reduces pressure ripples.

Less Aeration of Oil - Gerotor cavities fill over 180° of shaft rotation, causing smooth flow of oil, reducing aeration of the oil.

High Volumetric Efficiency - Gerotor pumps self prime and efficiencies often exceed 95%. Large inlet ports are active for over 180° of shaft rotation providing superior fill.

Long Life - Gerotor pumps have less moving parts, more bearing surface, and steel on steel oil flow path significantly reduces wear. Gear pumps have a steel gear with aluminum housing that wears creating an internal leak path. The relative RPM between inner and outer rotors, on a gerotor pump, is 600 RPM at 3000 shaft RPM resulting in less wear between the pumping sections.

Better Suction - While Gerotor inlet ports are active for more than 180° of shaft rotation, spur gear pumps have a displacement or volume change about every 7° of rotation. The 180° of port opening on a Gerotor pump gives superior fill capacity and suction.

Pump cavitation: What causes it?

Oil pressure is the result of several things. First, the pump must have an adequate supply of oil at the inlet side. Secondly, the pump must have the capacity to pump enough oil to overcome the "leaks" inside the engine and develop pressure. These "leaks" are due to bearing clearances, lifter bore clearances and top end oiling. If the supply of oil to the inlet side is not adequate due to small hose and fitting sizes, anywhere in the inlet hose, the pump cannot fill each chamber completely on each pumping event and the pump "cavitates", or works at less than maximum efficiency. Please note that the hose or fitting size is really the I.D. size of the hose or fitting. Some industrial hoses and fittings use the same thread sizes and wrenches, but the hole "I.D." is smaller than a comparable "AN" or high-performance fitting such as "EarlØs Performance Products" fittings. Typically, a small inlet hose size will cause the engine to see a loss in pressure at higher RPMs.

Can I run a Wet Sump engine and create vacuum in the crankcase?

In Wet Sump applications using PetersonØs Wet-Vac§ external pump or other manufacturer's vacuum pumps to create a vacuum in the engine, you will notice that as the vacuum increases, the oil pressure will decrease. This is the result of the pump having to suck the oil out of the pan, and in doing so, overcome the vacuum in the pan. As the vacuum increases, the force necessary to suck the oil from the pan increases and the pump is unable to completely fill on each pumping action, causing pump cavitation. Since the pump is pumping with less efficiency, due to the vacuum, the oil pressure decreases.

Wet sump or dry sump?

A Dry Sump system is preferable if the rules and budget allow a dry sump system. Some divisions only allow wet sump engines, and in that case, a Peterson External Wet Sump pump can provide externally adjustable pressure, more volume by adjusting pump speeds and more uniform timing by taking the pump drive off of the distributor. A great choice for those instances where you need to use a wet sump pump. Dry sump systems give you the ability to lower the engine in the chassis, due to a shallower pan configuration, control of windage and have a more positive supply of oil to the pump. Other advantages include: Externally adjustable oil pressure, the ability to speed up or slow down the pump, using different pulley and belt configurations, enabling the pump output to fit the need of the engine.

How do I choose the right sized pump for my application? 3, 4, or 5 stages?

In modern racing engines, control of windage (oil in suspension inside the engine) is one of the best ways to gain usable power. Evacuation of the crankcase can be better accomplished using multiple scavenge sections. All Peterson Dry Sump pumps, along with our competitors, use one pressure and 2, 3, or 4 scavenge stages. We have found that the Peterson 4 stage pump is as efficient as most 5 stage gear pumps, because of PetersonØs Gerotor design. Typically, 3 stage pumps scavenge with 2 pickup points in the pan, 4 stage scavenge with 2 pickup points in the pan and one pickup out of the lifter valley. 5 stage pumps scavenge with 3 pickup points in the pan and one pickup out of the lifter valley. Most pump manufacturers offer different size stages which pump more or less volume per rotation. Typically, the longer the section - the more volume

 

What is the torque specification on the draw rods?

The draw rods on Peterson pumps should be tourqed to 80 in lbs. Notice it is in inch pounds not foot pounds. These should be checked on a regular basis as part of the bolt check on the car.

 

Can I cap off an unused stage or tie two stages together?

No. Capping off an unused stage will result in pump damage and possible engine damage due to pump failure. The gerotor section needs oil for lubrication of the rotating aseembly. Also you may not "tee" two lines together as this can result in oil not being scavenged correctly. Each scavenge stage needs to have its own separate line running to the engine.

 

Can I use a check valve in the oil feed line to keep oil from running back to the engine when not in use?

No. A check valve in the feed line creates a restriction causing cavitation in the pump. If the car has sat use a drill to spin the pump before firing the engine. This will prime the pump and ensure that any oil that has gravity fed out of the tank will be returned and it will have a good supply.

 

Can I just weld a fitting to the side of the pan or use the drain plug for a feed?

No. A proper pickup is needed in the pan which will be a tube to a box with an open bottom or a tube with an opening along the bottom. The problem with a fitting welded in the side of the pan is it can become uncovered and suck air starving the pump and ultimately your engine of oil. Using the drain plug is not good either because it can also become uncovered in the course of a race. It can also create a vortex effect which can hamper proper scavenging of the oil.

 

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When plumbing in a breather can, to breath the engine, you should use at least a - 12 AN hose. The hose should run slightly up hill to the can so that any oil reaching the hose can run back down the hose to the tank. Be sure that the hose does not have any dips where oil can accumalate.

Remember- The air coming from the oil tank to the breather is a result of having multiple scavenge sections which pump a lot of air from the engine. If the breather hose is too small, the velocity of the air will increase over what it would be with a larger hose. This increase in velocity will tend to carry more oil droplets to the breather can. This is why a larer hose is better.

 

AN (Army-Navy) sizes were established by the aircraft industry and designate the outside diameter of rigid tubing that the corresponding fittings are used with. Each dash size equals 1/16 of an inch. (ie -8 AN = 8 x 1/16" = 1/2" OD of the metal tube) Each standard AN size has its own standard thread size. Since the tube sizes do not equate with the hose sizes, due to the variation in wall thickness, the ID of the hose and tubes are not the same. See the chart below for Earls Perform O' Flex hose and AN sizes.

 

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