eric-
I can' find the original post, took a long time to get back to you. you were going to adjust up the unloading pressure or try to shim the spring.
You've probably already done it or not. But just in case…..
The AE from HaldexBarnes never got back by phone but we emailed back and forth. I did not get a specific maximum pressure psi that the housing could take before damage. Higher psi limits the housing fatigue life and bearing life , not so much blow up the casting. Also, flexing internally causes it to wear faster.
This weekend, I took apart an older 28 Barnes I have. From inspection, there is not too much room to shim the spring and raise the pressure.
Under the allen head plug on one side is a piston. This senses the outlet pressure of the large (high flow) section. A long pin reaches across and pushes on the actual unloading poppet valve. On the back side of the poppet is the heavy spring with adjustment. When the force of the pressure on the piston overcomes the opposing spring force, the poppet opens and dumps the large section back to inlet. It is not like a relief valve, it unloads to inlet at very low pressure.
Screwing the adjuster in, or adding shims, increases spring force and raises unloading pressure, to a point. The limit is one of two things: the spring compressing solid into coil bind, or the outer edge of the adjusting screw hitting the poppet and physically holding it down on its seat. Either way, the poppet can’t open, or it may only have room to open a small amount. Then it won’t unload at low pressure, but cause all the oil to be forced across a small partially lifted space.
To get it to work properly would take a new spring. To be stiffer, it needs to be thicker wire diameter, and fewer coils. Then ends of the existing spring are squared and ground flat, so can’t just clip off some coils. Have to get a new spring. Associated Spring has about every possible combination in their line of heat treated springs, but I don’t have any idea where to buy one at a time. Have to be totally trial and error.
So, bottom line, try adjusting it up, but at some point you will hear it fully loading, or stalling, the engine. Stay well under that adjustment, so it can truly unload.
Or, it would be very easy to make it into a large single stage pump: just turn the adjusting screw fully in until it bottoms the spring coils, or until that adjuster hits the poppet. Then both sections are always working and the unloader is defeated.
How long will it last, will it blow……don’t know…..
k
I can' find the original post, took a long time to get back to you. you were going to adjust up the unloading pressure or try to shim the spring.
You've probably already done it or not. But just in case…..
The AE from HaldexBarnes never got back by phone but we emailed back and forth. I did not get a specific maximum pressure psi that the housing could take before damage. Higher psi limits the housing fatigue life and bearing life , not so much blow up the casting. Also, flexing internally causes it to wear faster.
This weekend, I took apart an older 28 Barnes I have. From inspection, there is not too much room to shim the spring and raise the pressure.
Under the allen head plug on one side is a piston. This senses the outlet pressure of the large (high flow) section. A long pin reaches across and pushes on the actual unloading poppet valve. On the back side of the poppet is the heavy spring with adjustment. When the force of the pressure on the piston overcomes the opposing spring force, the poppet opens and dumps the large section back to inlet. It is not like a relief valve, it unloads to inlet at very low pressure.
Screwing the adjuster in, or adding shims, increases spring force and raises unloading pressure, to a point. The limit is one of two things: the spring compressing solid into coil bind, or the outer edge of the adjusting screw hitting the poppet and physically holding it down on its seat. Either way, the poppet can’t open, or it may only have room to open a small amount. Then it won’t unload at low pressure, but cause all the oil to be forced across a small partially lifted space.
To get it to work properly would take a new spring. To be stiffer, it needs to be thicker wire diameter, and fewer coils. Then ends of the existing spring are squared and ground flat, so can’t just clip off some coils. Have to get a new spring. Associated Spring has about every possible combination in their line of heat treated springs, but I don’t have any idea where to buy one at a time. Have to be totally trial and error.
So, bottom line, try adjusting it up, but at some point you will hear it fully loading, or stalling, the engine. Stay well under that adjustment, so it can truly unload.
Or, it would be very easy to make it into a large single stage pump: just turn the adjusting screw fully in until it bottoms the spring coils, or until that adjuster hits the poppet. Then both sections are always working and the unloader is defeated.
How long will it last, will it blow……don’t know…..
k
