measure hydraulic pressure at any fitting?

[K5lwq]

interesting about leaving one in the system, you can know when you are approaching the limit, never though about that.

To the point about having multiple gauges in the system, that brings me back to my original question, which I still don't quite get. Assuming the gauge is dead headed, i.e. the end of the line, is the pressure the same throughout the system, so as long as that valve was actuated, the pressure should read the same whether it was measured at the loader valve, rear remote valve, or 3rd function valve?

As long as there is not another valve with a pressure relief then the pressure would be the same. Of course it will be different downstream of the valve you are using for the test.

 

[JCoastie]

found a quick video

 

[JCoastie]

when all else fails, rtfm lol

 

[rScotty]

interesting about leaving one in the system, you can know when you are approaching the limit, never though about that.

To the point about having multiple gauges in the system, that brings me back to my original question, which I still don't quite get. Assuming the gauge is dead headed, i.e. the end of the line, is the pressure the same throughout the system, so as long as that valve was actuated, the pressure should read the same whether it was measured at the loader valve, rear remote valve, or 3rd function valve?

I believe that your answer is "no, pressure isn't necessarily the same everywhere."
In the simplest hydraulic circuit the pressure would be the same everywhere, but then it could only do one type of work, and all the cylinders would have to extend or contract at the same time.

Think of blowing up a balloon. At first the pressure in the balloon is the same everywhere and it does one kind or work - it expands the balloon. But then you pinch off two areas and tie them off to make ears, then do the same for legs, and then you blow more pressure into it to force the remaining part of the balloon into a different shape. Now it is a carnival balloon animal with different pressures throughout. By tying off areas of the balloon you isolated them. Each one has its own different pressure.

A tractor hydraulic circuit does the same thing with devices called "flow preventers".
There are even one-way or backflow preventers. These will not allow pressurized fluid to flow back to an area of lower pressure. So the fluid under pressure is trapped in that circuit and remains at whatever pressure that outside forces - usually forces due to weight or springs - put onto that circuit.

Loader valves in the neutral position often act as flow preventers.

So if you put a gauge between the hydraulic pump and the input to the first device - often it is the input to the FEL control valve - it will show you the total pressure that the hydraulic pump is putting into the system. It won't show the max pressure it is capable of putting in, and it won't show the pressures in any "trapped system" within your balloon or your tractor. But that gauge will show the actual pressure at any moment that the pump is developing to overcome the total flow resistance of all the systems in the tractor.

enjoy, rScotty

 

[LouNY]

if the FEL control contains the relief valve, and hence controls the system pressure, I should still be able to check that pressure at any accessory port right? I sure would like to use a 1/2" quick connect, and I just can't do that at the FEL, they are 3/8" connectors, I can however use 1/2" at the 3rd function and the rear remotes.

Yes, it should be the same pressure. Most systems on the smaller tractors of today today have a relief on the loader valve for the system so your rear remotes being after that on the power beyond will read good. There could be a second relief on the rear remotes. That is more likely on a larger tractor with more flow.
This would only apply to an open center system as is found on the majority of utility and compact tractors. When you start talking closed center or pressure compensating closed center it can get a bit stranger.

 

[WranglerX]

interesting about leaving one in the system, you can know when you are approaching the limit, never though about that.

To the point about having multiple gauges in the system, that brings me back to my original question, which I still don't quite get. Assuming the gauge is dead headed, i.e. the end of the line, is the pressure the same throughout the system, so as long as that valve was actuated, the pressure should read the same whether it was measured at the loader valve, rear remote valve, or 3rd function valve?

On a open center system you will never see real time pressure reading.... Only time pressure builds is when there is a restriction to flow..... You have to deadhead "something in system" to cause back pressure, hence where the system's pressure builder (restriction) causes relief valve to open and bypass excessive pressure...

 

[oldnslo]

To the point about having multiple gauges in the system, that brings me back to my original question, which I still don't quite get. Assuming the gauge is dead headed, i.e. the end of the line, is the pressure the same throughout the system, so as long as that valve was actuated, the pressure should read the same whether it was measured at the loader valve, rear remote valve, or 3rd function valve?

Yes to this question on the based on the example below.

Example: pump is connected to FEL valve, Power Beyond of FEL supplies 3rd function, 3rd function power beyond supplies rear remotes, Power Beyond of rear remotes supplies 3 point.

With loader valve functions all neutral position and 3rd function in neutral position dead heading a rear remote will pressurize pressure line to FEL valve, power beyond of FEL valve, 3rd function pressure and power beyond and port on rear remote. It will not register pressure on any FEL work port or 3rd function work port.

 

[rScotty]

So now that we've discussed some of the ways that tractor hydraulics work, here is a question to use our hydraulic knowledge.

Suppose your tractor is real basic.... No HST, no FEL, no PS... just a basic tractor with a 3pt hitch and a nice heavy box blade.
You spend about $100 bucks and put two pressure guages on the tractor. One gauge is on a T fitting at the hydraulic pump outlet where it will show pump pressure, and the other on the 3pt test port back on the rear end so it shows pressure in the 3pt lift cylinder.

You are done spreading gravel, so you lift the blade up off the ground, put it into road gear, and then drive off towards home. All the work is done, and the 3pt is holding the blade in the air. Pretty typical....

What happens to the two gauge pressures while lifting the implement? Are they the same?
What do the gauges read when driving down the road with the 3pt holding the blade up?
What happens when you hit a bump or pot hole? Do the pressures change?

rScotty

 

[oldnslo]

When lifting should be similar.

Load lifted and static pump should just read line loss of pushing oil through system. Cylinder will show static load induced pressure.

While driving cylinder pressure will fluctuate when hitting bumps.

 

[LouNY]

So now that we've discussed some of the ways that tractor hydraulics work, here is a question to use our hydraulic knowledge.

Suppose your tractor is real basic.... No HST, no FEL, no PS... just a basic tractor with a 3pt hitch and a nice heavy box blade.
You spend about $100 bucks and put two pressure guages on the tractor. One gauge is on a T fitting at the hydraulic pump outlet where it will show pump pressure, and the other on the 3pt test port back on the rear end so it shows pressure in the 3pt lift cylinder.

You are done spreading gravel, so you lift the blade up off the ground, put it into road gear, and then drive off towards home. All the work is done, and the 3pt is holding the blade in the air. Pretty typical....

What happens to the two gauge pressures while lifting the implement? Are they the same?
What do the gauges read when driving down the road with the 3pt holding the blade up?
What happens when you hit a bump or pot hole? Do the pressures change?

rScotty

While lifting the blade the pressures will be very similar, once you stop lifting the blade the pump pressure will decrease.
While just traveling as you well know the pump pressure indication will be minimal, just line friction pressures from the fluid passing through the system.
If the test port in the rear is measuring the pressure trapped in the lift cylinder it will read the pressure that was necessary to lift the blade to the height it was lifted to, then while traveling and hitting bumps you could observe spikes as the heavy weight bounces on the fluid trapped in the cylinder.
Trapped cylinder pressure is usually not monitor as it would take relief valves and hoses from many locations. However larger tractors and loaders with "easy ride" functions using a precharged canisters "accumulators" to adsorb some of those spikes and shocks are available, they do impart a degree of vagueness and mushiness to loader controls.