How do you adjust a hydraulic valve?

WhiteRock · Mar 2, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

Junkman, I picked up on your statements earlier about engine speed. To me this is understandable. My claim (along with Henro's I believe) is that your system is working from pressure created by parasitic resistance. I wouldn't think of higher rpm as creating the pressure, but rather the higher rpm creating higher flow. As a result of the higher flow, the resistance causes a higher pressure proportional to the increased flow.

If your pressure rises from 200 to 1500 psi, with no load and idle to full rpm, I have to believe you have a serious restriction, crimped, bad hose or connector somewhere down stream. But... at this point I too am waiting to understand this conundrum.

The key would be to measure the grapple strength at idle versus full rpm. In a properly connected system the grapple strength would be the same at idle or full rpm. At idle it would move slower, but develop the same strength.

WhiteRock · Mar 2, 2005

I doubt that in theory there is such an animal as a constant current, variable voltage source. 

I feel I have to throw this in for EEs that may be new to hydraulics. I also found it to be a helpful analog.

There is indeed a frequently used concept of constant current. Many industrial controls use current loops for control and instrumentation. Current loops have a high immunity to voltage spikes, noise, etc.

Current is equivalent to flow, Voltage is equivalent to pressure, resistance is resistance. The pump (driven by the engine) sets the flow. If there is no resistance, there is no pressure. Electrically this means the voltage is constant at some nominal level. If the resistance increases for any reason, the pressure will increase to what ever level necessary to maintain the specified flow. The pressure(or voltage) increases until it hits the (electrical rail or) pressure relief valve. Flow will be maintained. In an electrical circuit the voltage can only rise to the power supply level.

So, extending the context of our thread, with no resistance there is no pressure. We shouldn't have much resistance doing no work. However, we know we have pressure, so where is the resistance.

Looking a Parker series 60, 1/4" valve flowing 4 GPM the pressure drop is a little over 30 psi. So connections can add up.

Henro · Mar 2, 2005

There is indeed a frequently used concept of constant current. Many industrial controls use current loops for control and instrumentation. Current loops have a high immunity to voltage spikes, noise, etc. 

WhiteRock,

I know most here don't care about constant current or voltage sources, and I hope they will bear with us for a moment.

Just to be clear, I was not disputing the fact that the constant current source is a great electrical analog to the constant displacement hydraulic pump. That is the way I look at it too.

What I was trying to say is that there are in electrical theory constant current and constant voltage sources, but you don't find them hooked in series. You generally have one or the other. Or maybe a combination in a more complex circuit, but not a hybrid mix.

 "a constant current, variable voltage source" would be analogous to finding a constant flow pump with variable pressure at its terminals. Hard to find. The pressure at the ports of a fixed displacement pump running at constant speed is a function of the circuit connect to the pump, not the pump itself. And a variable displacement pump changes the flow coming out of it, which will result in more pressure felt across a given flow path.

I guess what I was trying to say is:

A fixed displacement Hydraulic pump resembles a variable, "constant current" electrical source.

A variable displacement hydraulic pump resembles a variable, "constant voltage" electrical source.

Generally, you have one or the other.

All of which I fear is of little interest to most reading this thread! /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif

Banjo · Mar 2, 2005

Based on the new info, I'd also say it's the back pressure required to overcome all the various components in the complete hydraulic system that's providing the pressure for the grapple. This would go up as the flow goes up with engine RPM, so that's consistent with the observed behaviour. And if anything else downstream of the grapple valve in the hydraulic system is under load too, then that pressure is available to the grapple too.

Junkman,
in ( this 1500 PSI is registered at the end of the hose coming off the valve when the valve is operated.) is the valve you're referring to the CC one for the grapple? and the hose is one of the work ports that's normally going to the grapple cylinder? When you saw 1500 psi were there any other loads on the hydraulic system?

MMM, thanks for the info on the oil compression as the "friction" mechanism to convert the extra flow x pressure to heat.

Also, thinking about it again Henro you're right that there wouldn't be extra pressure on the "extra flow" output of the priority flow divider due to the steering pressure demands. The pressure there would be dictated by the resistance of all the downstream components (at the flow). Sorry about that everyone, the perils of late night "thinking aloud".

As others have said, this thread is a good learning/discovery experience.

cheers, Andrew

PS. Henro also wrote: ( (Maybe you meant to write a variable, constant current source? ))

Yup, I was a bit loose in the system/source terminology. Was since "tightened up" in later posts by others (It was the Mech Eng version of EE /forums/images/graemlins/grin.gif).

PPS. Henro's reply above came in while I was writing this. Yup I'd say in this area we're talking about the "close enough for all practical purposes" (if you know that joke) engineering not the strict electrical theory components. There's always resistance (second law of thermo I think ... "you can't even break even")! So "resembles" the theoretical is a good way of putting it.

WhiteRock · Mar 2, 2005

Henro, I agree, and guess this is what I was trying to say. I have seen a lot of folks reference this analog, so it may be more helpful than we think. However, if its reading sounds a little weird, I would recommend skipping. /forums/images/graemlins/grin.gif

"a constant current, variable voltage source" would be analogous to finding a constant flow pump with variable pressure at its terminals. Hard to find. 

I guess I was a little confused by this part. Hard to find? Isn't this exactly what our fixed displacement pump systems are? With the rpms set, the flow is fixed or constant (unless the engine can't maintain the power). Your next sentence says the pressure is determined by the circuit. Doesn't that make it a variable pressure at the pump?

Henro · Mar 2, 2005

I guess I was a little confused by this part. Hard to find? 

What I was trying to allude to, is that an electrical constant voltage source has voltage (electrical pressure /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif ) at its terminals, regardless of whether a load is connected to it or not.

The hydraulic pump, being more like a constant current source, would not have any pressure at its terminals (ports) until something is hooked to them. Just like a constant current source must be short circuited unless tied to an external circuit and has no voltage on its terminals in this case. Voltage (pressure) is a function of resistance the current is pushed through.

"Hard to find" was an (intentional) understatement... /forums/images/graemlins/shocked.gif /forums/images/graemlins/smile.gif

Isn't this exactly what our fixed displacement pump systems are? With the rpms set, the flow is fixed or constant (unless the engine can't maintain the power). 

Not in my mind. I see them very much comparable to constant current sources, and we are speaking tha same language here.

I was just splitting hairs, pointing out that a "constant-current variable-voltage source" does not really exist as an entity, as an electrical source, in my limited experience.

 Your next sentence says the pressure is determined by the circuit. Doesn't that make it a variable pressure at the pump? 

Well, the pressure can vary at the pump ports, just like the voltage is variable at the terminals of a constant current electrical source. But the source has nothing to do with that pressure/voltage other than providing the flow through whatever resistance that might be connected to it.

The flow through the resistance causes a voltage/pressure to be felt across the resistance to that flow. This is independent of the pump/CC source. The pump is happy to pump at zero pressure up to its design rating, just like a CC electrical source is happy to pump current through whatever load is connected to it, regardless of what voltage is developed across that load...

A related issue that came up recently is beer flow through the tubing between the beer keg and tap. The beer keg can be viewed as a constant voltage source (or a variable displacement pump), and the tap as a closed center valve...come to think of it, this winter has been a bad one, I gained a few pounds... I guess I could be considered the working cylinder in this picture... /forums/images/graemlins/shocked.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif

MMM · Mar 2, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

( AW68 )
AW68= Anti wear iso68 suitable for transmisssions, wet cluthes etc with corrosion inhibiter and anti foaming agent.

( single pump system )
Confusion might be there are 2 systems, not including a transfer pump inside tranny.

( !80 psi represents the drop across the steering diverter, that then feeds the OC FEL valve? )
I read 220psi on unloaded 17gpm tractor system at Multi Control Valve that supplys PS, hitch (through 5/8 steel tubing.), wet pto clutch, fwd/rev wet clutch, brakes, and lord knows what else.

( Do you know what your flow rate is and the size or your connector's )
180 psi at loader valve on separate 23gpm crank drive pump with 1.25" 2wire suction hose to 1.25 ported spin on, #140 suction filter, to 1,25NPT 90L at pump. From 3/4 anchor flange pump outlet is 3/4" 4wire terminated with 1"JIC into #14OR at loader vv.
Sectional 25gpm loader vv is PB rated and no sleeve needed at 7/8OR PB port supplying 2 Sun Pressure Compensated 0-16gpm PFD plumbed in series after loader valve that can each be taken offline whith 1"QDs when not needed. All aux return with main flow to 24X12, 16OR ported ,Thermal Tec cooler and 12v fan. and finally, 1" ported, 30mic ret filter. Both filter heads have differential bypass, but can't remember how much. Hope I didn't leave nothin out. /forums/images/graemlins/grin.gif

( surprised at the pressure delta across the various connectors )
Most connectors are rated for flow. I select them sized over my pump flow when possible. My general rule on QDs is select next size up from hose size. I use 1" QDs for 3/4" and 1/2" for 3/8 hose. This way I can grab them quick at auctions etc without a lot of research on flow specs, press drop, etc.

PineRidge · Mar 3, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

So Junk I heard word that even though your grapple works that you were told by someone "in the know" that it isn't plumbed for optimum performance. I'm thinking that more than a couple of regulars here have mentioned the very same thing as well.

Care to share that last bit of knowledge that you picked up recently, with the other members here at TBN? It seems that everyone and his brother is now following this thread and I'm sure they might like to know also......

Maybe we should all plan a road trip to CT and each of us could help with relocating the loader joystick so that it stays with your tractor when you lose the loader. We could then plumb the grapple off the power beyond port so it would do some real work. /forums/images/graemlins/wink.gif

JASTN70D · Mar 3, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

( help with relocating the loader joystick so that it stays with your tractor when you lose the loader
) Mike
I hear what you would really want to do is find a way to help Junkman with relocating the loader joystick so that it stays with the OPERATOR when he exists the tractor /forums/images/graemlins/shocked.gif

PineRidge · Mar 3, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

That's correct John and I can also recommend an excellent place for Junk to stash it. Eouch! /forums/images/graemlins/grin.gif