New Thumb Build

[firemanmike69]

Ok,so today I adjusted one of the relief valves until the ram stopped lowering. That worked but there is not much clamping pressure. I was told 1800 psi was the number to set the thumb at. Is this at an idle? Thanks.

The thumb should be set to what the manufacturer of the cylinder says it's rated for. The relief should be set with the engine at wide open throttle

 

[Xfaxman]

The thumb should be set to what the manufacturer of the cylinder says it's rated for. The relief should be set with the engine at wide open throttle

Why at wide open throttle?

 

[firemanmike69]

Why at wide open throttle?

The pump is flowing more oil at wot that at low idle, hence the pressure will be higher. Pressure is only restriction to flow. More flow =more restriction=higher pressure

 

[lcgoatboy]

The pump is flowing more oil at wot that at low idle, hence the pressure will be higher. Pressure is only restriction to flow. More flow =more restriction=higher pressure

Yes I have seen much higher pressure at wot but at 1800 it just doesn't seem like enough. I grabbed a rail road tie and it lost its grip. Why can't I just turn up the thumb pressure unit the curl is slightly the dominate function? The thumb cylinder is rated for 3000.

 

[Xfaxman]

The pump is flowing more oil at wot that at low idle, hence the pressure will be higher. Pressure is only restriction to flow. More flow =more restriction=higher pressure

I have a pressure gauge on a tee with quick connects that I can put inline with the circuit that I want to check.

All 4 of my different machines will reach relief pressure at idle, if you open a valve and let the cylinder go to the end of it's travel.

The relief pressure is the same at idle as it is at WOT. What you said is true, but the relief pressure happens when flow stops, so it can be adjusted at idle.

 

[firemanmike69]

Yes I have seen much higher pressure at wot but at 1800 it just doesn't seem like enough. I grabbed a rail road tie and it lost its grip. Why can't I just turn up the thumb pressure unit the curl is slightly the dominate function? The thumb cylinder is rated for 3000.

If the thumb cylinder is rated to 3000 psi and your other components are as well I'd run it at 3000 or untill the thumb force is slightly less than bucket curl which ever you prefer.

 

[skyhook]

Ok,so today I adjusted one of the relief valves until the ram stopped lowering. That worked but there is not much clamping pressure. I was told 1800 psi was the number to set the thumb at. Is this at an idle? Thanks.

I'm no expert, but I believe the relief has to bottom out when setting relief pressure.

 

[lcgoatboy]

Looked in the service manual today here's the layout of the valve and the functions


View attachment 410954

And if you're not reading the pressure directly at the attachment here's where you can read them on the pump


View attachment 410955

Hey Mike,would you happen to have the description of the valves on the first picture. I don't think that I have relief valves after all. The Allen screws that I'm adjusting does turn down pressure to the thumb but they don't hold pressure. I'm thinking about the cross over relief from Princess Auto that was suggested??? Thanks.

 

[lcgoatboy]

I would like to see a picture of the relief valve. I am pretty sure mine has a cross over relief valve near the base of the main boom. Its quite a large unit but I have purchased cross over relief valves from Princess auto for other projects and they where not $250. PA has a 10GPM Poppet style for 99 bucks.

Thanks, this is my next step.

 

[lcgoatboy]

So the allen key is what I adjusted and it does turn pressure down but wont hold. I think the cap below it is the spot for a relief. To the left of where the allen key is what looks like a relief for another circuit and I would say this is what I need.