Pressure testing difficulties

[LeeWorm]

JJ,

Thanks for the advice. Would you happen to know how long Northern Tool will accept exchanges? I still have all of the original packaging but I have had the valves for some time...just never got a chance to get started on this project.

Also, you had mentioned going from the last subplate T port to the 3pt IN port. Would this be the same as the PB port on the hydraulic block as this is where that last PB hose terminates?

 

[J_J]

Yes, that is correct.

 

[LeeWorm]

I have been reading quite a few of your replies on the subject and I need some clarification on the nomenclature. You have mentioned upstream and downstream in numerous posts and replies. Considering the layout that we have been discussing where you have the pump, block, FEL, and lastly the BH; is the block upstream of the FEL and the BH is downstream of the FEL with the pump being the source?

 

[J_J]

Yep, the hyd block is in the middle. Some tractors have them and other don't.

The hyd blk is a distribution assembly. The pump flow passes through the hyd blk and goes o the FEL,

The FEL returns the PB to the hyd blk for downstream valves, remotes, BH or 3pt.

The other stuff you said is correct.

 

[LeeWorm]

JJ,

I have been going over some of the things that we have talked about and the advice given thus far and there is one thing that I cannot wrap my head around.

When you say open center do you mean a true open center where all of the ports are interconnected in the center position or a tandem configuration where the P and T ports are interconnected in the center position?

When there is a relatively unrestricted flow through the system as with an open center system what is preventing the complete loss of pressure on the T side? Is there some sort of restrictor that provides some sort of back pressure? Even if it is only 50# or so?

 

[Tx Jim]

Granted I'm not J_J but one can't successfully have a "T" in an open center hyd system. Every component must be attached in a series from pump to sump.

 

[J_J]

On a valve without PB, the flow is IN port to tank port to reservoir.

The tank port on most valves are not rated for high pressure, only about 500 psi, and the presumption is that it will be the last valve in the flow path. Both pump flow and cyl flow pass through the tank port.

Nowadays, most new tractors have a dedicated high pressure port called PB for power beyond.

The tank port on new valves is for cyl expended flow.

So in an open center hyd system with remote and hyd blk, the flow path would look like this.

Pump, to hyd blk, to FEL, FEL PB back to hyd blk, to remote valve, to 3pt, to tank.

All tank ports can be teed .

If you have a BH, it plugs in after the remotes. If the BH has a PB port it can feed the 3pt. If it only has two hoses then the tank port goes to tank. You don't need the BH in most cases.

You don't want back pressure.

Running the tank port to another valve is never a good idea.

What you want is a one direction flow from pump to tank through all valves.

The first valve upstream that fully uses all the fluid leaves no for downstream operation.

The valves redirect the fluid to different hyd circuits.

 

[LeeWorm]

Okay so I completely disconnected the remotes from the hydraulics and connected the P back into the PB. However, I did install a TEE with a gauge to check the pressure and, just as before, the only time that I measured any real pressure was when pressure was directed to the 3pt hitch. I also hooked the gauge to the QC on the FEL connection as shown in the video at the beginning of this thread and read 2200 psi when engaging a function. This seems somewhat illogical to me. Can one of you help me understand what is happening that is preventing any real reading of pressure on the PB from the FEL to the 3pt?

 

[J_J]

I will tell you this, if you install the gage in a tee in the IN port of the FEL valve, you will read the pressure of any valve that is used .

I recommend doing this as a monitor and trouble shooting aid.

If a hyd gage is installed in the flow path, and you use the 3pt, you are reading the pressure that the 3pt cyl is developing.

If you have a gage installed downstream of the FEL, you will not read the FEL cyl pressure.

 

[skyhook]

If you have a gage installed downstream of the FEL, you will not read the FEL cyl pressure.

JJ, is the PB on a FEL valve considered to be "downstream" or will it also read the loader pressure when used.

 

[J_J]

Everything is downstream of the pump, so if you had a gage just after the pump, it will reflect any pressure developed by the hyd system.

Yes, PB is high pressure when any valve is using the fluid.

With no valve using fluid, the pressure in a PB hose is 0 psi or very little pressure.

A lot of people think of PB as beyond this valve, but the pressure can be read at the pump

 

[skyhook]

Thanks, JJ.

 

[LeeWorm]

Having gone through quite a few sites and reading through several threads, can someone confirm whether or not I am understanding this correctly?

In an OC system the system pressure stays relatively low when a function is engaged due to the fact that there is relatively no internal resistance within the circuit as the there is "free" flow between P and T or P and PB. The flow rate is relatively fixed but the resistance applied by the inertia of the load against the ram is what causes the measurable pressure increase within the system. Once the work is done, as in returning the spool to neutral, the pressure drops back down to some fairly small level.

That is putting it in my own words after reading the following excerpt from a thread on a talk.newagtalk.com forum:

"...1- the pump is usually a gear-type pump with a constant or "fixed" displacement,
2-the gear pump puts out a constant volume (fixed displacement) of oil for every revolution,
3-the pumped oil goes through a system of "open" valves that do not internally restrict or divert the flow of oil until the valve is activated, so the hydraulic system stays at a relatively low pressure until a valve is activated.
5- The pressure rise in the system is caused solely by the resistance of the hydraulic work to be done (i.e., the weight of the disk harrow against the hydraulic cylinder raising it)
6- when the work is done, the open center valve is returned to neutral, and the oil flow through the valve is unrestricted once again. The pump's flow doesn't change from neutral to full pressure; just the pressure in the system changes..."

 

[Tx Jim]

Yes that is correct as there's little to no pressure until a hyd valve is moved to direct oil to perform a hyd function.

 

[Xfaxman]

And the flow increases as RPM increases. If the system isn't worn badly the max pressure will be the same at idle as it is at peak RPM.