Thread: Air breather!!

How many of you guys have just a little hole for air breathing into your tank???

My built in axle/tank just has a 1/2 pipe plug with 1/16 holes drilled at right angles so the vent hole ends up horizontle, it still gets water in it if I leave it out in the rain. I have never felt how much air moves out by being an unbalanced cylinder, but now you have me thinking. Now I'm going to have to check.

Originally Posted by Blowncrewcab

My built in axle/tank just has a 1/2 pipe plug with 1/16 holes drilled at right angles so the vent hole ends up horizontle, it still gets water in it if I leave it out in the rain. I have never felt how much air moves out by being an unbalanced cylinder, but now you have me thinking. Now I'm going to have to check.

Thats exactly what I wanted you to do.....will be back later with more....

Mine's 3/8 pipe with a pair of elbows so the opening is facing down. Have not changed oil in many years, and no signs of contamination in it, so it must work fairly well.

Put this on with a tank change a few years ago.

If I put a vented cap of any kind on mine, it spits hydro fluid out the cap. I gave up and just put a non-vented cap on it. The fill neck is on the return side of the tank baffle and it's really churning in there. I've been thinking of putting a vent on the intake side, something small that I can open during operation and close when I'm done. Kinda like the water drain plug on a compressor tank, but mounted on top.

Ian

Tank breather....
When a double acting cylinder moves, the volume of the piston rod is the net volume change in the tank. Level lowers when cylinder extends, and level rises when cylinder retracts.
A 1” diameter (0.785 square inch cross area) piston rod that moves 2” per second (12 sec cycle time with 24” stroke), will make 1.57 cubic air per second, travel in and out thru the breather cap/hole.
At retract, air is leaving the tank when the rod volume of oil enters, and the force from the hydraulic pump is pushing the air out….The pressure relief valve is basically what limits the air pressure in the tank, as long as the tank or return line do not bursts.
At extend, air is entering the tank, and the atmospheric air pressure, which is maximized to about 15psi, is the only and limited pressure that can make air enter the tank.
If we have a restricted air breather, let’s play an example with a breather hole that is 1/16” (0.00307 square inch cross area), that is 1/256 of the cross section of the piston rod (1/16^2). That will mean that the air have to travel 256 times faster ( 512 inch per second) thru that breather hole without creating a pressure drop ……and of course we understand there is going to be an air pressure drop over that breather hole.
That pressure drop will then limit the supply of oil to the pump, and if the air pressure drop become high enough, the pump will cavitate, and we will also see a slower extend cycle.
What happens when we upsize the cylinder to a 2” rod (doubling makes cross section area 2x2= 4 times larger) and of course that will make the air have to travel 4 times faster to avoid pressure drop…..and that is even worse than the 1” rod example.
So now we need a 4 times larger (1/8” diameter) breather hole to stay status quo, with the 1” rod example.
The air velocity is the crucial part of the pressure drop, and we need to reduce the air velocity to avoid pump cavitation on cylinder extend action.
How do we know our air pressure drop over that breather cap/hole is acceptable?
It is possible to get close with math calculation, but the recommendable thing, is to mount a vacuum/pressure gauge (1/8” NPT) on the top of the tank. A gauge that shows both vacuum and pressure (-15 to 0 to +30psi)
Like this one….15$ inclusive the shipping….

Will be back about the suction filter....

Originally Posted by ray benson

Put this on with a tank change a few years ago.

thats the way to go benson.....weld a 2-4 inch tall (to get up from water and snow) piece of pipe pipe on top of tank, and with diameter enough to fit that breather cap.... thats the best you can do....love the strainer.....now you wont need a suction strainer....

Running a Donaldson TRAP breather on my TW-6. Keeps the dust and the water out!

My Huskee just has a pipe plug with a 1/16 hole drilled in it. Sometimes when it's used really hard it will squirt a little out.

Originally Posted by stihl sawing

My Huskee just has a pipe plug with a 1/16 hole drilled in it. Sometimes when it's used really hard it will squirt a little out.

1/16" to small air breather hole???
It do depend on the EXPECTED cycle time and the cylinder rod diameter. You might get away with it if have a real tiny rod diameter and a very slow extend cycle time/small pump....
and as I said earlier...on retract there is the whole engine/pump power behind the air, so it must come out or burst/blow something in the way....

I think for sure that 1/16"-1/8" air breather hole is way TOO small to be healthy for the system. That will definitely restrict air travel when cylinder is extending/splitting. with risk for pump cavitation and also decreased cycle time.

Originally Posted by AKKAMAAN

1/16" to small air breather hole???
It do depend on the EXPECTED cycle time and the cylinder rod diameter. You might get away with it if have a real tiny rod diameter and a very slow extend cycle time/small pump....
and as I said earlier...on retract there is the whole engine/pump power behind the air, so it must come out or burst/blow something in the way....

I think for sure that 1/16"-1/8" air breather hole is way TOO small to be healthy for the system. That will definitely restrict air travel when cylinder is extending/splitting. with risk for pump cavitation and also decreased cycle time.

Well i didn't mention there a two of them drilled in the side of the plug where you put the wrench on.

Originally Posted by AKKAMAAN

1/16" to small air breather hole???
It do depend on the EXPECTED cycle time and the cylinder rod diameter. You might get away with it if have a real tiny rod diameter and a very slow extend cycle time/small pump....
and as I said earlier...on retract there is the whole engine/pump power behind the air, so it must come out or burst/blow something in the way....

I think for sure that 1/16"-1/8" air breather hole is way TOO small to be healthy for the system. That will definitely restrict air travel when cylinder is extending/splitting. with risk for pump cavitation and also decreased cycle time.

How would a small breather hole increase cyle time or cause pump cavitation? The air will simply be pushed out faster through a smaller hole than it will a bigger hole.

Originally Posted by Thickskin

How would a small breather hole increase cyle time or cause pump cavitation? The air will simply be pushed out faster through a smaller hole than it will a bigger hole.

Obviously I havent been clear enough...LOL...
Please read the whole thread before commenting, I am here repeting what I said per 04-07-2010 02:20 AM, but in a little different way....

Well, first I want you to try this.....grab one of this tiny straws that ar abot 1/16" diameter, put it into your mouth, ducttape your nose, and try to breath fast......What is easier??? get the air in or pushing it out??

The air is not coming out faster through a smaller hole (when cylinder is retracting), it is coming out with higer velocity. A smaller hole is a restriction, that will build pressure inside the tank. This is actually positive to prevent suction cavitation.

But whe cylinder is extending cylinder it works the opposite way. If pump tries to pull more fluid volume from the tank than what is coming back from the system, then this volume differens have to be compensated with AIR. If pump take 10CUI of fluid per second, then 10 CUI per second of air have to enter the tank through the breather hole. If that breather hole is to small and even clogged up with dirt, IT IS NOT GOING TO HAPPEN. We will then get a pressure lower than atmospheric pressure, and that could cause cavitation if we get low enough pressure.....

Read about cavitation here