Mini excavator thumb - relief valve question

[ptsg]

On my setup, the relief valve for the thumb just dumps to the tank and I've never had any issues with it.

As far as relief valves, Surplus Center has plenty of those and I'm sure others will have too, like Summit hydraulics.

The style of relief valve the OP used is more common in Europe and looks like Canada get those too.

 

[Stumblebum]

I found a valve that will work --->Surplus Center.
I wonder if the dump port of it could be tee-ed into the other port on the hydraulic cylinder to eliminate the negative pressure in it.
An inline check valve would probably need to prevent back-flow when the relief valve is closed.
If the check valve idea wouldn't work, how could oil be provided to prevent that negative pressure ?

​

 

[ptsg]

I found a valve that will work --->Surplus Center.
I wonder if the dump port of it could be tee-ed into the other port on the hydraulic cylinder to eliminate the negative pressure in it.
An inline check valve would probably need to prevent back-flow when the relief valve is closed.
If the check valve idea wouldn't work, how could oil be provided to prevent that negative pressure ?

​

Technically you can but you can only push the thumb with the bucket so far, because the rod side of the cylinder won't take the full volume of oil coming from the extending side.

 

[rScotty]

On my setup, the relief valve for the thumb just dumps to the tank and I've never had any issues with it.

As far as relief valves, Surplus Center has plenty of those and I'm sure others will have too, like Summit hydraulics.

The style of relief valve the OP used is more common in Europe and looks like Canada get those too.

I wonder if your your Directional Control valve for the thumb has a regenerative circuit in it? Some DC valves have that as an internal feature.

 

[ptsg]

I wonder if your your Directional Control valve for the thumb has a regenerative circuit in it? Some DC valves have that as an internal feature.

Oh definitely not. It's about the most basic valve one can get. It's literally a block of steel with a spool inside and an handle on top. Doesn't even have a relief valve built it. (I have one right after the pump though)

I don't think it's that big of a deal having the relief valve for the thumb cylinder just relieve back to the tank. Some excavators out there just rely on the work port relief valves for this purpose and those will dump to the tank as well.

 

[rScotty]

Oh definitely not. It's about the most basic valve one can get. It's literally a block of steel with a spool inside and an handle on top. Doesn't even have a relief valve built it. (I have one right after the pump though)

I don't think it's that big of a deal having the relief valve for the thumb cylinder just relieve back to the tank. Some excavators out there just rely on the work port relief valves for this purpose and those will dump to the tank as well.

Sometimes primative is OK. And it allows the opportunity to make simple improvements on operation, safety, & efficiency.

 

[Stumblebum]

I haven't done anything yet in regards to installing a relief valve until I replace stabilizer section in the backhoe control valve.
It has either crack in the body, or a worn out or damaged spool.
I was able to use that circuit for my thumb by plumbing a diverter valve into it.
I am waiting on delivery of said section.
After I get it repaired I will be able to determine if the thumb is still still able to force the bucket further open.
If it does then I will reseal the bucket cylinder piston even tho it has low hours since it was resealed the last time.
The way it is now the bucket cannot force the thumb cylinder to retract.
I do know that Caterpillar thumbs cannot force the bucket to open further nor can the bucket force the thumb to retract.