Can the hydraulic system get air locked after a fluid change

[oldnslo]

Over filling should not cause a pump operation problem.

 

[rScotty]

I just changed fluid and filled to manufacturer specks.I'll try oldnslo's suggestion of forcing air into resivoir to see if that will prime the pump.Any other suggestions would be much appreciated.

I would be real concerned about running a hydraulic pump dry for more than a few seconds. What I would do is the traditional mechancs prime:

First of all, we know that a good hydraulic pump will self-prime quickly unless there is a suction air leak in the intake line. So that is almost certainly the basic problem. Usually it is due to old suction hose with splits at the hose ends. But at this point it has been run dry enough so I'd prime it first even if you do find and fix the suction air leak.

To prime any pump, get yourself access to the outlet of the pump either at the pump or somewhere at the end of the pressure hose from the pump. Then connect a few feet of clear tubing with a funnel on the end, hang the funnel above the tractor as far as you can, and pour the funnel half full of whatever low viscosity trans/hydraulic fluid* you are using. Let it stand a few hours and enough fluid should seep past the pump vanes to fill the system.
With luck, the funnel trick might even show where the suction side air leak is happening.

Reconnect everything and start it up. If you are not getting pressure to the hydraulics well inside of a minute, then shut it down.
Luck,
rScotty
* I gotta put that in bold. Hydraulic fluid is pretty thin stuff. 90 wt won't work.

 

[sandman2234]

It has been said several times, but I am going to repeat it...don't let that hydraulic pump whine, get the problem fixed because it will burn up the pump in a very few seconds!
David from jax

 

[rScotty]

It has been said several times, but I am going to repeat it...don't let that hydraulic pump whine, get the problem fixed because it will burn up the pump in a very few seconds!
David from jax

Boy is that ever right. I said, "inside of a minute"...but that was describing a situation where there is some oil because it has been back-fed through the funnel.
Even so, If it were mine, and didn't make pressure in a five or ten seconds I'd quit and find out why. Then prelube the pump through the outlet port before trying again.

Always inspect first the cleanable screen filter in the sump if that tractor has such - about half of them do. If it has one, always clean that first, particularly if the reason for the fluid change was to get rid of milky oil because of water intrusion.

Then check the suction hose and screw-on filter gasket. After that, the suction side fittings. I've never seen a suction blockage be due to a bad screw-on filter, but I have seen aftermarket and OEMs that didn't seal well at their base gasket ring.
Luck,
rScotty

 

[Leonard malone]

Thanks for the info .I'll try the funnel.Thanks

 

[arrow]

I just changed fluid and filled to manufacturer specks.I'll try oldnslo's suggestion of forcing air into resivoir to see if that will prime the pump.Any other suggestions would be much appreciated.

More than likely You have air in your system. It needs to be bled so l wouldn’t add any more air. Air can be compressed and liquids barely. The air you already have in there is being compressed and that point of compression is interrupting the pressure of the liquid to be building as it should.
Open up a hydraulic outlet to bleed the system.

 

[rScotty]

Look. Let's back up & try to unconfuse things a bit. The problem is the OP has done a hydraulic oil and filter change and now his hydraulic pump is not moving fluid. So in his original question in the title of this thread the he asks,

"Can the hydraulic system get air locked after a fluid change"​

The answer is that in an open center hydraulic system like his Kioti and most small tractors use, the hydraulic system cannot get air locked because it is not a sealed system. The sump is always open to the atmosphere by way of the vented sump. Hydraulic fluid cannot get "air locked" because one end of the circulation is open to the atmosphere. Any air gets moved along - or not - to the sump and escapes to the atmosphere. That's not to say that there can't be trapped air in the system causing other effects, but it won't cause an "air lock".
An "Air Lock" is not why his pump isn't working.

BTW, the radiator and cooling system are different.
Modern tractor cooling systems ARE SEALED SYSTEMs. They are not open to the atmosphere unless the system overheats. They definitely do have to be purged of air during filling because once the radiator cap is tightened down that system is sealed. It is not open to the atmosphere, so with the radiator cap in place there is no way for air to escape. In a sealed cooling system a trapped air pocket doesn't always mean the entire flow is blocked, but it can be. It will create a "hot spot". So there definitely are ways that an air lock can cause heating problems in a sealed system.

Hope this helps,
rScotty

 

[arrow]

Look. Let's back up & try to unconfuse things a bit. The problem is the OP has done a hydraulic oil and filter change and now his hydraulic pump is not moving fluid. So in his original question in the title of this thread the he asks,

"Can the hydraulic system get air locked after a fluid change"​

The answer is that in an open center hydraulic system like his Kioti and most small tractors use, the hydraulic system cannot get air locked because it is not a sealed system. The sump is always open to the atmosphere by way of the vented sump. Hydraulic fluid cannot get "air locked" because one end of the circulation is open to the atmosphere. Any air gets moved along - or not - to the sump and escapes to the atmosphere. That's not to say that there can't be trapped air in the system causing other effects, but it won't cause an "air lock".
An "Air Lock" is not why his pump isn't working.

BTW, the radiator and cooling system are different.
Modern tractor cooling systems ARE SEALED SYSTEMs. They are not open to the atmosphere unless the system overheats. They definitely do have to be purged of air during filling because once the radiator cap is tightened down that system is sealed. It is not open to the atmosphere, so with the radiator cap in place there is no way for air to escape. In a sealed cooling system a trapped air pocket doesn't always mean the entire flow is blocked, but it can be. It will create a "hot spot". So there definitely are ways that an air lock can cause heating problems in a sealed system.

Hope this helps,
rScotty

Air can be still trapped in an open system Scotty.
Although less likely than in a closed system.
Customers like to save money and do fluid change service themselves and who can blame them. Not to accuse the op of improper procedure as I have no proof of that either way, We have experienced in these situations where the customer has started their tractor being minus the proper amount of fluid with the idea they would get more fluid later on or worse, where the customer, after a few quarts thought they had to start their tractor thinking to get the fluid moving.
The insufficient amount of fluid can cause tiny air bubbles or entrained air and keep coming because of turbulence. Another cause would be tiny leaks in the system constantly drawing in air such as a misaligned filter gasket. Yet another would be high points in the hydraulic system creating dead air pockets.
Ordinarily, this air as you describe in an open system, can be jettisoned with merely a few turns of the steering wheel saying everything else is tight.
If this pump has failed, no amount of coaxing will get the air out.

If it were me, Id start all over again. 1. Drain and save the replacement fluid. 2.Undo the filters making sure of proper gasket integrity and alignment then re-assemble filters.
3. Check all hydraulic unions to make sure of tightness.
After thats been done, refill the tractor to proper level being careful not to get any splashing that the glug-glug coming from the fluid can will cause. This can place unwanted air into the system. Refill with the spout at the top and a funnel sticking out of the fill hole to mitigate this. The first thing to do is to move the steering wheel back and forth after start up. It would be a good idea if the filters were preloaded with a bit of fluid even though most of these on smaller tractors are horizontally placed.
I know this is rather a pain but it will be a telltale if the pump has indeed failed. If not, then it's a cheaper and a simpler fix even having to repeat the fluid change procedure rather than springing for a new pump.
Hopefully the op's pump is still intact.

 

[rScotty]

Air can be still trapped in an open system Scotty.
Although less likely than in a closed system.
Customers like to save money and do fluid change service themselves and who can blame them. Not to accuse the op of improper procedure as I have no proof of that either way, We have experienced in these situations where the customer has started their tractor being minus the proper amount of fluid with the idea they would get more fluid later on or worse, where the customer, after a few quarts thought they had to start their tractor thinking to get the fluid moving.
The insufficient amount of fluid can cause tiny air bubbles or entrained air and keep coming because of turbulence. Another cause would be tiny leaks in the system constantly drawing in air such as a misaligned filter gasket. Yet another would be high points in the hydraulic system creating dead air pockets.
Ordinarily, this air as you describe in an open system, can be jettisoned with merely a few turns of the steering wheel saying everything else is tight.
If this pump has failed, no amount of coaxing will get the air out.

If it were me, Id start all over again. 1. Drain and save the replacement fluid. 2.Undo the filters making sure of proper gasket integrity and alignment then re-assemble filters.
3. Check all hydraulic unions to make sure of tightness.
After thats been done, refill the tractor to proper level being careful not to get any splashing that the glug-glug coming from the fluid can will cause. This can place unwanted air into the system. Refill with the spout at the top and a funnel sticking out of the fill hole to mitigate this. The first thing to do is to move the steering wheel back and forth after start up. It would be a good idea if the filters were preloaded with a bit of fluid even though most of these on smaller tractors are horizontally placed.
I know this is rather a pain but it will be a telltale if the pump has indeed failed. If not, then it's a cheaper and a simpler fix even having to repeat the fluid change procedure rather than springing for a new pump.
Hopefully the op's pump is still intact.

Yes, I agree with all those mechanic's techniques, arrow. They are all good to do.

But I believe you are making the mistake of answering a different question than the OP asked.
The OP's question was not whether air could get trapped in an open hydraulic system. Of course it can. We all know that. His question was whether that trapped air could cause the hydraulic system to become "air locked" and not able to flow.

It don't think that can happen. Imagine if the entire system was full of nothing but air. Everything is at atmospheric pressure except for a pressure drop across the pump.
In that case the pump will still draw fluid from the sump, pump it through the system, and back to the sump again. The fluid would be carrying some entrained air along, but not necessarily all of it. The hydraulic system cannot become "air locked" as long as the sump is open to the atmosphere.
rScotty

​

 

[arrow]

Yes, I agree with all those mechanic's techniques, arrow. They are all good to do.

But I believe you are making the mistake of answering a different question than the OP asked.
The OP's question was not whether air could get trapped in an open hydraulic system. Of course it can. We all know that. His question was whether that trapped air could cause the hydraulic system to become "air locked" and not able to flow.

It don't think that can happen. Imagine if the entire system was full of nothing but air. Everything is at atmospheric pressure except for a pressure drop across the pump.
In that case the pump will still draw fluid from the sump, pump it through the system, and back to the sump again. The fluid would be carrying some entrained air along, but not necessarily all of it. The hydraulic system cannot become "air locked" as long as the sump is open to the atmosphere.
rScotty

​

Ok. I gotcha. Air block vs air massed.
Perhaps it borders on the semantical for the op. Air trapped/air blocked. If pressure is insufficient, it is not an air pocket that is blocking. Pressures are simply insufficient to get the pocket moving.
Entrained air can cause cavitation and thus the pump whine and thus insufficient pressure build up.
If this speed is fast enough, this entrapped air won’t get a chance to rise out of the oil.
It just keeps circulating creating turbulence in turn causing more tiny air bubbles.
Hence my advice to start again.
The method of refill becomes more important than ppl think. Slowly is key.