Logic would dictate that, all other things be constant (orifice size, ball, etc.), reducing the spring pressure would proportionally reduce the output pressure. That said, I've gone down a lot of dead-end streets based on what I considered logic. Do you know the manufacturer of the valve itself; their tech support department could probably give you a quick answer. Otherwise, a basic text on Fluid Mechanics could prove helpful.

Sounds like you're really close!

 

Maybe I missed it but do we know who manufactured that pressure reducing thingamajig for the pump? Presumably these should be off-the-shelf items from somebody if we could find out who the somebody was/is?


Doug

 

Do we at least know who is the OEM supplier of these pumps to jaguar?

 

The standard method of reducing power steering pump pressure in a Mustang pump used on a kit car was to cut part of a coil out of the relief spring. One had to cut a portion out of just one coil and try it. Very tedious, and unscientific. Hopefully you can match a new spring to the 85 bar spring and get approximately 1100 PSI. How will you be measuring the pressure, teeing in a line and gauge? If you are successful, we'll all owe you a beer.

 

I promise we won't need to crack a book on this one (but it's there if we need it). On these ball-and-spring thingys, the math is nothing more than this: the opening pressure is that at which the spring force on one side of the ball matches the force from fluid pressure on the other. So ...

spring force = fluid pressure x area of hole where ball seats
= 1600 PSI (observed) x .0094 square inches (my measurement)
~ 15 lbs.

So opening pressure can be changed by changing spring force and/or size of the hole; proportional to each if the other is held constant.

These valves have no markings indicating a manufacturer, and are so simple, and use such an odd thread, that I think Power-packers just made their own. Burping these out compared to some of the fancy machining they have to do inside the pump body would be nothing.

In searching for replacements, I haven't seen anything like them, especially the wierd 1/4" x 28 parallel thread. (Everything commercial is fancier in one way or another.)

[Edits for late arriving posts]

- The pumps are made by Power-packers. In my experience, not too interested in talking to car owners.

- I don't have sufficiently accurate pressure measuring gear; I'm hoping someone who does will eventually do a measurement. No need to use a "T"; there's a port in the pump body available for this.

 

Q: how do you convert one of our 110-Bar relief valves to 85-Bar?
A: Just turn the screw, dummy!

It turns out we will not need new springs or new parts of any kind to reset the internal relief valve pressures. Please take a look at the photo of the pump body in Post #1. Hard to see because of the light and the angle, but on the 85-Bar valve the orifice is protruding a little more from the top of the valve body than on the 110-Bar valve. It has been threaded in a little less, compressing the spring a little less, changing the relief pressure from 110 to 85 Bar (1600 to 1230 PSI). Not much of a difference by eyeball ... about 1 thread (1/28").

Inside the parts are identical, so nothing will need to be changed out. All we need is a rule for how much of a screw turn produces a given change in relief pressure.

I've still got one undisturbed 110-Bar valve to use as a standard, and will be able to work this out. Within a week or two, I hope, but some travel is on the calendar. My best SWAG right now is ~ 400 PSI per turn (don't write that down, please!).

When the "400 PSI per turn" estimate is refined and nailed down, we will be able to set or re-set any valve at will from any starting point. If someone wants the ram circuit regulated to the same pressure as the latch circuit, he just sets the valves on each to the same point (not beneficial IMO, but someone asked about it).

I think that's everything.


Almost forgot ... And kudos to Sklimii who saw early-on that the valves looked to be adjustable! I didn't.


(p.s. Given this result, I'm inclined to abandon the effort to find substitute drop-in replacement valves. The threads were driving me nuts anyway. But if anyone feels they would prefer that idea to adjusting the in-place valves, please make a post here.)

 

Wow, sometimes the solution is staring you in the face. So all you have to do is adjust, reassemble, and test at the gauge port? Time to buy a 2000 PSI gauge and adapter.

 

I've got such a gauge, but trouble is a mechanical gauge is too sluggish to accurately capture the rapid pressure pulses that happen when the latch opens and closes (those are the highest-pressure events). I learned this the hard way a couple of years back.

There is data-logging gear that uses a transducer, and puts out a nice pressure v. time chart, resolution to 10s of milliseconds. Sooner or later, I'm hoping somebody with access to such gear will adjust their valves, test, and show us the data. But IAC the basic technique of adjusting spring tension in a spring-and-ball relief valve as a way to vary relief pressure is a pretty standard practice.

 

Did the screws appear to be locked in anyway?

I'd expect an adjustable valve like that to be secured in some way after setting maybe with a centre pop on the threads or thread locker.

 

They sure were locked, Norri. Take a look all the way back at post #5 please.

One thing still to be worked out is how to re-lock a valve after an adjustment. I'm thinking drill a small hole in to the orifice from the side, and use aviation safety wire (or similar), but for sure open to suggestions.

 

I would think you could use a punch to lock the thread, my question is how to unlock them?

Great work here

 

I had rather limited forum access when the thread started so I didn't grasp that, sorry!

I'd tend to agree with Jandreu and use a punch after you got it set where you want it.

 

Jandreu, Norri

Never have done this so ... can you explain for me a little about using a punch to lock the threads. Reversible?

BTW, I dropped a factor of 2 in making that qiuck-and-dirty estimate above. (But that wine was good!) It will probably work out to be on the order of 800 PSI per screw turn ... about two turns from zero to 1600 PSI. Still just a rough estimate though.

 

Just to be sure I understand what threaded screw to adjust the pressure we are talking about....I assume this is the brass screw with the hole and slot on the end of the valve in post #1. If so after setting the pressure take a pointed punch, position it at the point where the brass screw threads meet the valve body on one side and whack it. This will deform the threads to prevent them from moving.

Now as I originally asked, how are they locked...I suspect the same way I just described which will be problematic to release but can be done with a small bit very carefully.

 

Yes, the brass screw you described. But, as to how they were originally locked, I'm afraid everything I know is in that photo. It looked to me like maybe a pin had been driven down in there, but I don't have experience with this.

To free them, I did carefully drill as you described.

I think when we reset them it would be better to do something more easily undone. Maybe a new very small hole in the brass screw -- going in through the hole in the valve body that was drilled to free them -- then safety wire (or similar, nothing fancy needed). What do you think?

 

Looking at the valve (separated from the pump--thread #1) I think it is evident that the manufacture first drilled a counter sunk point to just above the threads, so a punch (or press) could be used to set the screw. Trying to set the punch onto the threads, because of the thick housing of the valve, would have been impossible without the counter sunk.
I believe that if that point is drilled out, there wouldn't be enough metal left in the housing to provide a point for another punch/press.
Using a vise to hold the valve, then the correct driver to fit the slot in the screw exactly (such as hollow ground drivers found in "gun smithing" tools), should provide enough force to turn the screw beyound the punch point.

Chuck
05/XK8 Conv. 1-200

 

OK I was thinking the original lock was on the end at the threads but as described I now see what you are referring to. Could the countersink hole where the original lock punch was made, after drilling out to release the threads, be tapped for a set screw?

May be an issue with pressure leaking past the threads with the set point drilled thru, don't know?

Also to the number of screw turns per pressure equation, at the estimated 800 psi per rotation it would take about 3/4 of a turn to reduce the pressure to 1100 psi. By measuring the screw in relation to the end of the valve on the other valve for the rams and comparing this same measurement on the 1600 psi valve this could be confirmed.

 

Man I don't know. I would think though, that this adjusting screw is just a solid bolt with a whole drilled down the center length of it---for what reason I haven't a clue.
I would think however that this valve is just a simple screw, pushing on a spring, which presses on a ball bearing which is in a seat that controls the pressure of the fluid.---(Bing Go!). after the pressure is reached as set by the screw, spring and ball bearing, it releases the over pressured fluid which passes by the ball and back into the fluid holding tank via THE HOLE DRILLED down the center of the bolt.
I'm an old Army helicopter pilot, so don't take what I say as gospel. It could all be wrong, but I would bet my old gray cloth flight suit on it.
So drilling a hole through the counter sunk hole and through the bolt, wouldn't hurt a thing, other then giving the over pressurized fluid another way of getting back in the tank.
What crew think, kid?

Chuck
05/XK8 Conv. 1 of 200

 

CS, makes sense...

 

It's as CS said, a simple ball and spring, components shown in #38. The brass(?) adjusting screw does indeed have a hole through its center, and that is the only way for fluid to get out when the valve opens. Looks to me like the hole was sized to act as an orifice, but the size can't be critical.

The only "seal" then is the one between ball and seat, which we won't be disturbing. So I'm feeling OK about going the safety-wire route, but somebody please yell if they see a problem.