Hydraulic high pressure gauge

[Ronray]

Where and what kind of hydraulic high pressure gauge that will go up to 3000 pounds should I get? It would be just for my personal use on my marklift Model 62 manlift.

And the service manual said to connect it to a high pressure port, but I don't know where I would find the high pressure port. Would it come directly off of the main hydraulic pump? And if so, I don't know how I could get the main hydraulic pump to pressure up and see the gauge while I am operating the ground controls or aerial controls.

There is a gage attached to the proportional valve manifold, but I think that is for pilot pressure, which normally runs between 100 and 500 pounds. Picture attached.

 

[Junkyard]

My preference is Cat. Seems like the $25 gauges from the hydraulic shops don’t last as long. Cat runs about $65. 8T-0859 is a 3,600 psi gauge.

What are you wanting to test? There are different points for different issues.

 

[Cmark]

Not familiar with your machine, but from what I can see in the photo it looks like that gauge may be plumbed into the main supply line for that valve. If so, it would read max pump pressure when one of the functions was dead headed.

Oh, and +1 on the Cat gauges.

 

[kshansen]

Picture's not clear but that gauge might be a 6,000 psi gauge so it should do the job.
Something about that valve and even the marking on it remind me of the Snorkel lift we had at the quarry.

If you want to be able to watch that gauge while working something I'd just pop it off by the quick connect and take it to any good hose shop and tell then you want to have a hose so many feet long installed between the gauge and quick connect.

Also ask them if the can supply a new quick connect and the fitting to attach the Cat gauge when you get it.

My rule of thumb for gauges is to select one that has a maximum reading of approx twice the pressure you want to read. That gives you a little safety margin if a relief valve is not set right or there is some other problem.

 

[John C.]

That's a 6,000 PSI gauge. There is also a number four JIC male Tee fitting at the bottom of that plumber's dream below that gauge where you can attach a hose and run it out to where could see it if you didn't want to pay $50 for another quick coupler.

 

[Ronray]

Thanks everyone!

Cmark so if that gauge is plumbed into the main supply, then it would be showing the pilot pressure when a function is not engaged, correct?

What does Deadhead mean? Would that be for example if you keep the control lever engaged after the extension boom has extended all the way out?

Yes it is a 6000 pound gauge, but it seems to be filled with a clear fluid, oil? To prevent corrosion? I'm wondering if I remove that gauge to attach it to a hose, if that oil in the gauge would flow out, since it is mounted vertically?

Great idea on the hose. I'm thinking I could just attach it to a 25 foot hose, and just coil it up and leave it attached to the hose inside the engine compartment?

 

[Cmark]

The question is IF it's the supply line. Hard to be sure from the partial view in the photo. The larger hose on the left, does it go to a pump?, and is there another hose on the opposite end of the valve going to the tank? If so then yes, it's a supply line. To deadhead would indeed be to, for example, extend a cylinder all the way and hold pressure on it, then the gauge would show the pressure going to that cylinder.

With the caveat that I'm not familiar with this machine, I would say that the gauge would NOT indicate pilot pressure. My best guess right now is that the small hose going into the valve bottom left of the picture is pilot oil.

 

[Cmark]

Oh, and yes, better quality gauges are filled with oil, mainly for damping. On top there should be a rubber bung. As long as it's in place the oil won't run out.

 

[Ronray]

Thanks Cmark! Yes actually that big hose comes directly from the main pump and there is a hose at the other end of the proportional valve manifold that goes back to the storage tank.

Okay, so I assume that holding pressure after deadhead will not blow out the hydraulic hoses. Normally when the engine is idling with no functions engaged the pressure gauge shows about 100 to 200 lbs, but if I look at the gauge 5 or 10 seconds after extending the boom for example, as long as it takes me to walk around the machine to look at the gauge, it will show a thousand pounds pressure. Does that sound normal?

And what do you think of this idea, I could just put my cell phone in video mode or use a video camera aimed at the pressure gauge and record the readings while I'm operating the functions?

 

[Cmark]

IF your hoses are in good condition, holding pressure on them will not be a problem. If they're getting a bit old and crusty, it's at your own risk

Usually I would expect the pressure to drop back to close to zero immediately a valve is put back to neutral, but once again, I'm not familiar with that machine. What exactly are you trying to achieve here? Do you have a specific problem?

Good idea about videoing it.

 

[John C.]

It's usually glycerin that they put in the gauges. It stays clear and won't freeze. It's also good to know what kind of a pump and hydraulic system you have. An open center parallel passage system will most times have a positive flow gear or vane type pump while a closed center system might have a variable flow piston pump. It will make a difference on what you see on the gauge and how the machine is acting. I haven't worked on that brand of man lift before so don't know what you have.

 

[Ronray]

Cmark, I'm wondering if my drive wheel motors are low on torque because of low hydraulic pressure from the main pump. I have another thread going which I haven't gotten any replies on entitled " boom lift Drive Wheels torque fade". I just posted a schematic diagram of the torque drive motor on that thread. It's a Cessna 20800 variable piston motor assembly.

 

[Ronray]

Okay so I was able to read the pressure by recording the gauge with my cell phone video. With no function engaged, the pressure was about 200 lb, but when I engage the boom lift function the pressure jumped up to 2500 lb. And when I engaged the drive wheels, the pressure also jumped up to 2500 lb. And the right side wheel continued to spin, but the left wheel stopped turning. Is this normal pressure for the drive wheels? Would this rule out the main hydraulic pump as being the cause for loss of torque in my drive wheel motors?

 

[Cmark]

Looking at the photo you posted in one of your other threads, unless I am mistaken, it looks like the component which splits the hydraulic flow to the motors is a plain manifold. If that is the case, both motors will see the same pressure but the one seeing the least resistance (traction) will spin.
Do you have a hydraulic schematic for the machine?

 

[Ronray]

Thanks Cmark. Attached is a screenshot of the hydraulic schematic and a closer up screenshot of the hydraulic motor area on my 1980 marklift 62. The third screenshot is a hydraulic hose schematic in the same manual but it is dated 1986 and it is showing a two speed shift cylinder on each wheel, whereas my 1980 model has just 1 two speed shift cylinder operating both wheel motors.

I could also just upload the entire PDF manual at 12 megabyte if that would be allowable on this forum.

 

[heymccall]

The gizmo I circled splits the supply oil between the two drive motors, very much akin to an open differential in a drive axle. Whichever motor has no traction will steal all of the oil, by design, leaving the other motor motionless.

 

[kshansen]

The gizmo I circled splits the supply oil between the two drive motors, very much akin to an open differential in a drive axle. Whichever motor has no traction will steal all of the oil, by design, leaving the other motor motionless.

And if my poor skills at reading hydraulic schematics is right that would only be effective in on direction. I recall the Snorkle Lift we had at the quarry had a flow divider valve in the lines from the control valve to the motors. If memory serves me right it was suppose to send approximately the same amount of oil to each motor, kind of like a limited slip differential.

It may have only been when in say a low speed situation, been a few years so I'm a bit cloudy on this!

 

[kshansen]

Not that it will help with this machine but did find the drawing for the Snorkel Lift, not the same kind of schematic type drawing. In it you can see the two different flow dividers in the drive circuits forward and reverse:

 

[heymccall]

And if my poor skills at reading hydraulic schematics is right that would only be effective in on direction.

The other direction doesn't have anything but a tee.
Thing I circled may very well be just a flow restrictor then. Either way, that schematic shows that the motor with the least resistance gets all the oil.

 

[Cmark]

The component circled contains two orifices which appear designed to allow both motors to have pressure at the same time, but I'm not sure what the Down Arrows denote. Bear in mind that when the motor is run in the opposite direction, the oil from the motor still had to go through these orifices so the effect will be the same.