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Read our primer articles on Desiccant Breathers and Oil Filter Carts.

The easiest way to get a correct answer is to follow the filter company's advice. They have the expertise and experience to provide you a quick and reliable answer. They will also expect you to buy their filters, but you can shop around for prices that make sense to you, now that you understand the flow-size relationship that they recommend.

I also find it is important to buy from reliable companies, like Pall, Parker, Donaldson, etc. I have been to Chinese factories to see filters being made. Their test equipment looked like it was just for show, and not for testing. Testing takes time and a desire to produce quality products. These factories also did things like drag the filter medium from the payoff spool, across the floor to the pleating machine. Every filter was potentially contaminated.

Also, be sure you follow their advice on pore size. The pore size should be small enough to clean the oil to the level you need, but not so small that spark discharge becomes a problem.
Hi mohanraj,

I think the best route will be to consult directly with a filter company. Your concern as an end user should be the cleanliness target you would like to achieve in your fluid.

As a guideline you should be filtering out all particles larger than what your oil film thickness is. Typically hydraulic systems operate with fine tolerances so your cleanliness targets are going to be something like 16/14/12 depending on the application.
Originally posted by mohanraj:
Hi ,

I am new to hydraulic filters, Is there any calculation to find the surface area of the filter element for a specific flow rate

My comment may not be timely, but still....

There are two factors of great significance that were not mentioned:
1. Does your note refers to an in-line or off-line filter system?
2. What is the viscosity (and type) of the oil you try to filter?
Dear “mohanraj”;

The reason I was asking you those questions is, to remind you of something you may already know, that the main purpose of in-line filters is not to filter the oil you are operating with. Their purpose is to primarily protect sensitive equipment (i.e. proportional valves) from a sudden wear potentially generated by intake pumps in the system, providing that the bulk oil is filtered to a cleanliness level suitable for the tightest clearance in the system. The notes posted by both, Ray Gomes and Perry Thiessen are very informative and valuable. I will join them in saying that filter companies may be the best source to find the calks you are looking for. However, finding the “right” ratio to optimize oil flow and surface area of a filter (to reach the best filter efficiency) are much more important for off-line filters than the in-line filters. Nonetheless, an over-sized surface area of an in-line filter element will prevent any possible oil’s pressure drop upstream of the filter due to thickened oil during cold start, and minimize electrostatic buildup and discharge.

Dear mohanraj,

Please as you attempt your make it better project, for a reciprocating engine, Clean oil is best but Dirty oil is always better than no oil. o not attempt to put a very fine filter in series with the Lube Oil Pump, because these filters will usually plug quickly then you either wind up with no oil(if there is no bypass) or dirty oil (if there is a bypass.

It sounds like you have a very high dirt load coming into the engine. If this is the case, a three prong strategy is recommended.

First double up on the Air inlet filter. The engine manufacturer should be able to help here. Next leave the engine manufacturers filter alone as this will keep the boulders from getting into the bearings. Next use one of these self powered centrifuges to take out the 20-50 micron particles (This unit will take 10% of the flow, and return it to the sump.) Next install a very large depth filter in Parallel with the centrifuge to remove the 3-20 Micron Fine material. This strategy should work well to keep you at NAS Class 4 or better.

Change the all filters and clean the Centrifuge (Liner Papers are available) Monthly, and test the oil monthly to keep the oil in good condition. If you maintain NAS2 for three months back off to a 2 Month Schedule. Also Please top up regardless of what happens at the Manufacturers regular schedule. Also weigh the sludge every time you clean it and put the KG in the engine log book.

Good Luck

Let me know what happens

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