# 1953 Ford Jubilee back pressure valve



## Rshuttl (May 2, 2014)

Can anyone tell me how the back pressure valve function? I have no hydraulic pressure when I take the plug out of the auxiliary cover. No oil reaches there at all but the pump is pumping! I have removed the cover and oil raises 6 to 8 inches above the case when the machine is running with a little throttle! I inspected the internals of the hydraulic safety valve and it looked good! Now I suspicion the back pressure valve could be the problem! Is this a symptom of that valve not functioning properly? With the auxiliary cover remove I blew air into the port going down to the hydraulic and the draft worked fine! Any assistance is appreciated!


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## HarveyW (Sep 15, 2014)

Hello Rshuttl,

A pressure relief valve is installed in hydraulic systems to protect against accidental pressure spikes. It would be set to pop open at the maximum design pressure for the system, like 2500 psi for example. 

A back pressure valve is installed in hydraulic systems to maintain relatively constant pressure within part of the system, like the lift piston pressure. On the NAA, I think the backpressure valve is set at 2000 psi, so when operating pressure exceeds 2000 psi it is popping open and closed to maintain approximately 2000 psi pressure.


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## Rshuttl (May 2, 2014)

HarveyW said:


> Hello Rshuttl,
> 
> A pressure relief valve is installed in hydraulic systems to protect against accidental pressure spikes. It would be set to pop open at the maximum design pressure for the system, like 2500 psi for example.
> 
> A back pressure valve is installed in hydraulic systems to maintain relatively constant pressure within part of the system, like the lift piston pressure. On the NAA, I think the backpressure valve is set at 2000 psi, so when operating pressure exceeds 2000 psi it is popping open and closed to maintain approximately 2000 psi pressure.


Ok, so we have the in line safety valve, the back pressure valve and the unloader valve that has a specific ring that can fail and cause hydraulic loss or random reaction! I have no oil or air escaping from the plug fitting removed from the front right side of the hydraulic system plate. With that plate off I applied air to the hydraulic valve and had full draft reaction! I have looked at every internal piece other than the back flow valve and I am trying to understand it before taking it on! Is it your opinion that the back flow valve would keep pressure from getting to the top fitting? This last couple months with this Jubilee have been quite and education on hydraulics and trouble shooting! Thanks


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## HarveyW (Sep 15, 2014)

Do you have a service/shop manual? I would get an I&T FO-19 shop manual. 

First thing you need to check is your hydraulic pump. Your tractor is 68 years old, and your vane pump is ancient. Piston pumps replaced the vane pumps many, many years ago. And yes, there is a piston pump for an NAA tractor. 

The manual should provide a troubleshooting section for the hydraulic system. Follow their directions. You will likely have to pull the lift cover.


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## Rshuttl (May 2, 2014)

The back pressure valve seem to be in an open position and flowing all the time back into the oil reservoir! Is it possible dirt has the valve partially open not allowing the system to build pressure? Thru the process of elimination this seems to be the culprit! Any thoughts or comments are appreciated!


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