School me on Pressure Gauges

[Richard]

A bit of an update.

Yesterday, I cobbed the three gauges into a board with cutouts and got the third T mounted. Hooked gauges up and went out for a test.

First thing I noticed.... the right (recently rebuilt) motors gauge was boucing around like a kid in a bouncing house. The left (second motor on that same circuit) was very silent until it hit some tall grass then it bounced up.

I'm guessing this means the second gauge might have been too loose and fluid was getting by much easier than the first one. I dismounted and tightned it down 1/2 turn. Now, they both started to act .....how to word this.... "more calm". They still bounced but it wasn't one being schizophrenic while the other was dead.

Oh, side comment, I had put zip ties on the three 30' of hoses (each was 30' long) I didn't know how much I might need to allow for pulling when in a turn. I had wrapped it around the grab bars to climb into seat.... used zip ties to keep it together.

I did NOT however, account for the turns I was doing to loosen it up a bit.... just enough that one of the hoses got under the lip of the mower and hooked by the blade. Interestingly, the hose wasn't chopped up (it was destroyed) but rather looks like someone tried to skin it alive.

Shut everything down so I could remove all hoses and now that it seemed to at least be in better balance, try again.

Went to cut and got around the corner when, looking back (as I'd been doing a lot of) I see a geyser of oil spraying vertical.

I'm starting to smile now as it seems the Field Cutting Gods must not want their 5-6 foot high field cut....

The "T" that I put in, sits below a 4x4x2 junction box and is near impossible to FIRMLY attach without a crows foot. I do not have an approximate 1 3/4 crows foot..... so with everything hot to touch, used my cresent wrench to inch it backwards and removed it, putting the hose directly back to the input.

Note to self, I need to get a set of large crows feet wrenches.

Went about cutting and it still lays the VERY tall grass over from time to time but otherwise is getting close. It might not be exact. Heck, it might not even be "in the ballpark" but that said, the ballpark seems to at least be in view.

The life of the experiment on the gauges was very short lived but was enough to allow me to make that adjustment. I'll replace the hose and try it again but with even more attention to the routing of the hoses. Seems the blades really don't care what confronts them.

 

[5030]

Not a clue about what you are doing but pressure gages come 2 ways. Filled and unfilled. For hydraulic applications I recommend a filled gage, filled with a dampening fluid which eliminates needle bounce and eventual failure and I'd install gages that are capable of indicating at least a couple hundred PSI higher that your maximum pump pressure.

 

[Richard]

Yep, got filled gauges and they still bounce. PSI rating is 2x that of the stated pressure relief. (3,000 gauge for 1,500 pressure relief and 5,000 gauge for 2,500 pressure relief)

Check!

 

[5030]

Most are glycerin filled and the viscosity of the glycerin will impact needle bounce. Ie: the heavier the fluid is, the less needle bounce there is. Nice thing about filled gages is they all have a fill plug on the top so you can remove and replace the fluid if you so desire. Something I did on my spray rig. I dumped out the original fill and replaced it with thicker viscosity motor oil and so far, other than the slight amber color, they have been working just fine.

 

[Egon]

There are also separate dampers that are placed in line with the Gage.

 

[aircommuter]

Yes a gauge snubber would help you out.

 

[Timmy1957]

A hyd system that is moving will show the pressure required to make it move. An extending cylinder or a hyd motor. Once the system is loaded it slows down the movement and pressure goes up. (Pressure is resriction to flow) If the cyl or pump are stopped, then pressure goes to the max of the releif valve. If the work load is lowered and the hyd oil starts moving then the pressure comes down.
i have worked on hydraulics for 30 years but i have never owned a hyd drive bushog. I see no reason to have a gauge on it. 2nd It you are going in one motor and out to a 2nd motor, then if the 2nd one loads up then both gauges will rise. If the load on the 1st motor rises then it should raise its gage but not the second one because it is downstream of the load.

 

[Timmy1957]

A hyd system that is moving will show the pressure required to make it move. An extending cylinder or a hyd motor. Once the system is loaded it slows down the movement and pressure goes up. (Pressure is resriction to flow) If the cyl or pump are stopped, then pressure goes to the max of the releif valve. If the work load is lowered and the hyd oil starts moving then the pressure comes down.
i have worked on hydraulics for 30 years but i have never owned a hyd drive bushog. I see no reason to have a gauge on it. 2nd It you are going in one motor and out to a 2nd motor, then if the 2nd one loads up then both gauges will rise. If the load on the 1st motor rises then it should raise its gage but not the second one because it is downstream of the load.

I was surprised (i never owned one) to hear that each motor fed the next motor, instead of each motor having its own supply. But if you have motors that require 10 gals per min(making that up) and they are fed thur 1st to 2nd to 3rd, it only takes 10 gpm to fullfill their need. But if you run a supply hose from the pump to each motor then you would need 30 gpm to maintain the speed. 4th. as somebody mentioned the relief valve is not to set your system pressure but as a safety device. If you need 1500 psi in a system, set the pump to 1600 PSI and the relief to 1700. (just an example) Note if your pump is set at 1700 psi and the relief is 1500psi then you are making 200 psi and dumping it. Thats why a lot of hyd systems are too hot and overheating. Sorry hard to explain on here.

 

[aircommuter]

That’s a close description except pressure is resistance to flow. Restriction is a different matter. BTW I have 58 years.

 

[Flogger]

Almost sounds like a bad accumulator. Surely there is something to absorb the spikes created in that type of application.