Filler Breather Size 3

[RobertHasty]

Hello forum members,

I would like to know if anybody here is thinking whether their filter breather is sized correctly?

Please share with me some guidelines when determining the size of a breather.

Robert.

 

[hydtools]

Depends somewhat on whether or not you are powering single-acting cylinders or continuous flow components. How much and when fluid leaves and returns to the reservoir. Relatively stable fluid levels require smaller breathers than high flow, and rapidly changing levels.
My choice is as large as is practical to suit the application.

Ted

 

[kcj]

Ah, the most neglected filter in most systems.

Also depends on if you have an accumulator in the system. flow rates can increase dramatically for short periods. Worst case: accum bag ruptures or leaks, some N2 goes into the return line back to tank when the system shuts down, and severely foams up the oil/fluid. The froth gets into the breather element, then the pressure drop for outgoing air is increased 10x or 100x over the pressure drop of pure air as it was designed for. Tank goes like a sausage, or blows the gaskets around cover or lid if you are lucky.

Larger breathers also go longer between service, more dirt holding, and less pressure drop especially in the inlet direction when absolute pressure at the pump suction can be affected.. The spin on adaptors to use a 1 inch return filter element seem to work well if you don't want pressure/vacuum feature. I think Zinga makes an adaptor with P/V feature.

On larger tanks, with accum in system, I use as big a breather as possible, usually two or more in various corners, well baffled underneath to try and prevent the froth from getting to the breathers, and often add a 2 or 3 psi cracking check valve, quite large in size, with a vent pipe to the floor. Overly conservative, but all things that have bitten me in the past.

kcj

 

[RobertHasty]

On larger tanks, with accum in system, I use as big a breather as possible, usually two or more in various corners, well baffled underneath to try and prevent the froth from getting to the breathers, and often add a 2 or 3 psi cracking check valve, quite large in size, with a vent pipe to the floor. Overly conservative, but all things that have bitten me in the past.

Thanks for this post. I think that this bolded part is a guidance for most of us. Once when it hits You, You don't risk anymore.

 

[Oldhydroman]

Hi Robert

For some reason the site wouldn't let me upload my contribution earlier today, but, if not too late, here's my two cents worth:

It's fine to say "as large as practical" or "overly conservative" but how do you actually arrive at a number? Well first of all you have to know what the maximum air flow rate is for your system (either ingress of egress). Be very careful with accumulator systems - there can be a sizable air ingress when the accumulators are being charged because there is no oil coming back to the tank during this process. Similarly discharging the accumulators causes a significant air egress without any oil going into the pump. Anyway, once you know the air flow rate you need to factor it up to match the in-service conditions.

Multiply the worst case air flow rate by 1-2 if the application is a clean room or laboratory with little air borne dust, where there is an air breather clogging indicator and there is continuous monitoring of the degree of clogging.

If there is an average amount of air borne dust (normal shop floor applications) where there are no clogging indicators but the elements would be changed every time the hydraulic filters are changed, then multiply the worst case air flow rate by 3-6.

In harsh, dust laden environments (foundries, construction machinery etc.) where there are no clogging indicators and where there is a low likelihood of regular air breather maintenance, then multiply the worst case air flow rate by 7-10.

With your corrected air flow rate, consult your manufacturer's datasheet showing the pressure drops across the elements [choose an element no coarser than your hydraulic filters] and select one that has a pressure drop of no more than 0.01 bar (0.15 psi). Well, that's what I do anyway.

DOL

 

[hydtools]

Manufacturers seldom publish pressure drop through the filter. Calculate the maximum expected fluid flow into or out of the reservoir and use that as a figure to compare to manufacturers' published data to select a breather or breathers size. Then select a filler/breather.

Ted

 

[Oldhydroman]

Hi Robert

Ted is quite right. But remember always that the manufacturer of the breather knows nothing about your machine's environment - so you have to artificially amplify the air flow rate to enable you to pick a suitable size element. Oh, and the breather manufacturer knows nothing about the construction of your tank either, so his choice of a permissible pressure drop may not be suitable in your application.

I know some manufacturers don't show a graph of pressure drop versus flow rate, but there are plenty who do (Hydac, Donaldson, Parker and many others). So, if you really wanted to use the product made by the "I-can't-be-bothered-to-help-you tank breathers corporation" and they can't/won't send you the graph that you need in order to do a proper selection, then simply find a reputable manufacturer's datasheet and pick a breather that shows the same pressure drop for the same air flow as the one without the graph. Standard [non-pressurized] air breathers are pretty simple in their construction and I doubt very much that the laws of physics change between manufacturers. You will then be able to perform the proper engineering based selection which you started off asking about.

Personally though, having done the necessary research to find a datasheet with a graph on it, I would be tempted to thank that manufacturer by actually buying their product. At some point in the future you might have to justify your choice of breather, and using engineering first principles to claim equivalence between two different manufacturer's products might be beyond the understanding of your adversary. Breathers are very important but they aren't expensive. My advice: don't waste your time with products that aren't properly supported and documented.

DOL

 

[IceStationZebra]

One negative with more breather capacity is that infrequently used system may have an increased chance of moisture problems. Then again if they are very infrequently used it won't really matter! ISZ