Do I need to drain air from hydraulic system?

[swampdog]

On my Hitachi EX270LC, I'm changing the Full Flow Filter Element in the hydraulic tank and the hydraulic Pilot filter. I'm not changing the hydraulic oil.

Can anyone tell me if it is necessary to do anything to extract air from the hydraulic system after changing these two filters? The manual warns against starting the machine with air in the hydraulic system and talks about filling the two hydraulic pumps with oil and draining air from the pumps. It also mentions "running the cylinders and swing motor uniformly for 10 to 15 minutes" to drain air from the hydraulic circuit.

I don't want to damage the system and can use advice about this. Thanks for your help.

 

[salesrep]

You should take the steps to release any air.

 

[swampdog]

I agree. But does air enter the two main hydraulic pumps when one changes those two filters? Or is it only necessary to bleed the pumps when one changes all the hydraulic oil? What's the usual procedure?

 

[qkoop]

I have never heard of having to bleed the air out after changing the filters.The hydrulic tank is higher than the pump so even after you change oil it fills up the suction inlet and the air goes to the top of the tank.

 

[John C.]

As stated, any air in the filters will just go on top of the hydraulic oil in the tank.

You need to bleed air off the pumps only when you drain the tank or pull the pumps off the machine.

There is a procedure for when you change cylinders but it only involves moving them a little at a time back and forth until the air is moved out. It will end up in the reservoir and be relieved through the breather.

 

[ncbschzzt]

The tank filter is only a return filter no need for bleeding air. However be careful when removing the breather cap as it will be pressurized. Make sure you bleed the air from the tank before removing the tank filter. Only real concern, I would also check the bottom of the filter seat and look for any metal debris.
You said two filters, what two are you talking about. There is only one return filter, and a suction screen. The screen doesn't usually need to be replaced just cleaned. I use a drill and some brake clean. Simply pull out the suction screen it is a oring sealed fit and insert the long bolt into the drill. I put the bolt on a vice and start it up while spraying brake clean. Works out pretty well, saves a little money.
I would like to know what two filters you are talking about also.

 

[special tool]

The tank filter is only a return filter no need for bleeding air. However be careful when removing the breather cap as it will be pressurized. Make sure you bleed the air from the tank before removing the tank filter. Only real concern, I would also check the bottom of the filter seat and look for any metal debris.
You said two filters, what two are you talking about. There is only one return filter, and a suction screen. The screen doesn't usually need to be replaced just cleaned. I use a drill and some brake clean. Simply pull out the suction screen it is a oring sealed fit and insert the long bolt into the drill. I put the bolt on a vice and start it up while spraying brake clean. Works out pretty well, saves a little money.
I would like to know what two filters you are talking about also.[/QUOTE



The Hitachis have A large real filter at the bottom of the tank.
It is compression fitted with an 0-ring which comes in the kit.

But the second filter he is talking about is the pilot filter which cleans the oil right after it leaves the pilot pump.

 

[ncbschzzt]

It sounded like he was talking about two filters in the tank, and I was making sure he is not replacing the tank suction screen. This is not necessary unless the machine had a catastrophic failure. That screen is attached to the bottom of the long bolt that you would see if you removed the tank cover that has the breather attached to it. The return filter actually doesn't sit at the bottom of the tank, that is the suction screen. The return filter has a cradle that runs about half way down the tank and the cover for it doesn't have a breather on top. That is the filter that needs to be changed.
I don't think he was talking about the spin on replaceable element pilot filter.

Part number for tank return filter AT147343
Part number for suction screen 4210224 (don't have to replace this screen just clean)
Part number for pilot filter element AT186554

 

[swampdog]

The second filter is the pilot filter. I went ahead and changed both filters (full flow and pilot) yesterday. No metal filings or other unusual deposits were found on the filters.

I partially filled the pilot filter cannister with oil when putting it back together but did not bleed any air from the system. No problems were noted on startup; all hydraulic functions work well.