InsaneHydraulics - Sergiy Sydorenko © 2009-2011 All Ridghts Reserved
And once again I am talking about suction filters...
Suction filters and strainers have been around for
decades, and this, probably, is the main reason why there are still
people, who think that use of suction filters is beneficial. Use of
suction filters in modern hydraulic installations can only be explained by blind tradition following and nothing else.
There are many articles on the web about this topic,
and what I am writing here is no news, but every now and then I stumble
upon a new project, well designed by apparently experienced engineers,
and yet there you have it, a practically unserviceable suction filter
inside an oil tank, just like a bird poop on a freshly washed new car
smack in the middle of the windshield.
The most common answer I get when I ask what was the main
reason to justify the use of suction filtration, is something like "the
equipment will work in dust (sand, sawdust, flour, dry paint, dirt,
etc...) contaminated environment, so some extra filtration can't hurt,
right? To prevent the dust from entering the pump, right?" Well, wrong!
First of all, suction filters, as a rule, will have high
micron ratings and low beta ratio (filtering efficiency), which
by definition make them a piss poor filtering solution. And secondly,
even a filter with the largest screen can condition suction line, and
actively reduce life span of the pump.
If you want to know exactly how a pump feels when a
suction filter is used, try to run a ten miles marathon wearing this.
Those of you who had done military service will know what I am talking
about. So if you are still defending the use of them suction filters,
you should consider wearing this at all times, as it also will protect you
from particle contamination, (and, as an additional benefit, will give
you a mysterious S.T.A.L.K.E.R. Shadow of Chernobyl touch).
The only place where you might consider (consider!) installing an oversized
suction filter, would be a closed circuit charge pump inlet. Mainly
because in this situation we have low flow rates and sensitive
equipment conditions. But I, personally, prefer pressure side
filtration for charge pumps, which is a way better option as it allows
the use of lower micron rates and more efficient filters.
Instead of worrying about not allowing the dirt to enter
the pump, you should worry about not allowing the dirt to enter
the OIL. If you are projecting a hydraulic system that will allow
enough oil contamination to need a suction filter, than that is a
I am aware that there ARE no-other-exit situations that,
in fact, mandate the use of a suction strainer. I have seen myself
in such situations, and, against my principles, have applied
suction filters for large open circuit pumps, BUT those were the
situations when the oil tank construction was made against all common
sense by people, who had absolutely no idea on how a hydraulic oil tank
is made, with NO possibility to rectify the situation and the
urgent and undisputable need to put the equipment in service. The
obvious disadvantages of suction filtration were overpowered by the
benefit of the pump not exploding five minutes after the startup due to
welding balls inside the oil tank. Even in such situation you should
oversize the filter. In fact, you should always oversize suction filters!
Of course, this is the technical side of the problem.
There also is the commercial side. From the commercial point of view a
suction filter is another serviceable element a client will have to pay
for in the future. As long as the equipment passes the warranty period
without major failures, the use of suction filters is also a "polite"
way of reducing sevice life of a pump, which a client will most probably
buy at the same shop he bought the equipment.
So, suction filters are good for business and bad for
pumps (with very-very rare exceptions), consider this next time you design or order a piece of