Thanks much, Max. I will install this on my car, but I do not have equipment to record pressure readings.


IMO, the alignment of the stock relief valve setting with what has been measured as peak pressure (~1600 PSI) leaves little doubt what will happen with a lower-pressure valve, at least for the close-latch operation which is the one that makes the most pressure. But it would be nice if someone could do some measurements and publish them to remove all doubt.

(Nice history of rides you have there, BTW!)

 

Yeah, and if I still owned many of those rides today, I'd either be very rich or totally broke (probably the latter). I think I saw in a previous post that you live in South Jersey. I used to live outside of Glassboro and moved to West Chester, PA a few years ago. You're probably not that far away from me, and I might have a friend who can loan me a pressure gauge for the grand experiment.

 

Dennis and Max, you are going in a direction that seems very logical.
If Max can get the equipment for testing, all that's left is the "T" connection.
Are our hose connections anything other than standard metric?
It all makes me wonder, how low could you go?? and all still function. Unfortunately, you would need a whole handful of valves.


Wayne

 

I just have to pop in here and point out that none of this is really new. Gus and Walt had not only exhaustively gone through all of the intricate pressure measuring of the system but also packaged a kit with a pressure reducing valve. Let's at least give some recognition to their work here.

Doug

 

Wayne,

A couple years back, lots of measurements were taken on stock and modified systems. Scanning old threads will turn up that history (the good, the bad, the ugly). It's known that ~ 1000 PSI is the max pressure needed. I like 1100 PSI because it leaves a little wiggle room if a particular car has a balky system.

The required gear for testing is around (there's a metric tap in the pump body so no "T" required). If someone would publish a measurement that would be great, but even without that ... We know now of the internal 1600 PSI relief valve that explains the "stock" 1600 PSI pressure. (No prior mention of this valve that I know of. If someone knew of it but still opted to add a parallel, external relief circuit ... not for me to explain.) Anyway, A lower-PSI internal valve must make for a lower peak pressure, as with an external valve.

On the history of the problem, people's past efforts and their commentary, I'm going to try like hell to stay silent. Except for a quick nod to my old collaborator, Reverend Sam.

 

Wayne,

I don't know of too many (if any) people who have lent their technical expertise, time and patience as Gus has in the service of this forum. I've consulted his website many times to try to find solutions to the various glitches in these wonderful cars. No slight or disrespect to Gus should have been construed, nor any diminishing of the value of his solution to the inherent problem with our convertible top system.

We are an extended family of tinkerers (else why would we own these cars?). Inclusive of this is the right to try to "re-invent the wheel" and very often go down dead end streets in the exercise of our intellectual curiosity. I thought Dennis07's idea was not necessarily better or worse than Gus's, just different in that it only limited the pressure to the latch mechanism rather than the entire pump output. If it works, than it's another tool that any or all of us has the option to use. If it doesn't, no one else's time will be wasted and this thread will fade into obscurity.

That's all I really have to say on the matter (everyone applauds). Thanks again to the Forum for making the ownership of these cars both feasible and wonderful.

 

Just to clarify a few points that the PRV by LSI does reduce the pressure to the Latch and the rams. See the chart on this link that supports our findings

Link JagRepair.com - Jaguar Repair Information Resource

 

On regulating latch and ram circuit pressures with the internal valves:

While changing out (or modifying) the internal relief valve for the latch, we could just do the same for the ram circuit. Worthwhile? The effect on ram pressure would be quite small or zero. But if someone wants to match up the max pressures in the two circuits ... won't hurt anything. Either way, we're retaining the pump's original design, where the two circuits can be regulated to different pressures.

The cost would still be a fraction of that for an external kit (which is restricted to a single pressure limit for both circuits). And there is still a possibility of zero cost ... if we can learn to reset the stock internal valve(s).


A little far afield, but the effects of the voltage reducing resistor on peak pressure and pressure gradient are discussed here.

 

Thanks for the clarification, Gus. I was operating from (faulty) memory in my last post regarding your pressure relief valve solution. The information in your link is incredible both in detail and accuracy. Wish I had your focus and patience.

 

Thank you! I try to provide accurate and tested information on my page.

 

I'm hoping someone here can give me a little guidance about threads.

Our stock internal relief valves thread into a non-tapered hole in the pump body. The threads on the valve itself are likewise non-tapered. 1/4" x 28 tpi thread pitch. The threads themselves do not need to provide a seal; there is a compression washer between valve and pump body.

[1/4" x 28] matches an NPT standard thread. But as I look at candidate NPT replacement valves, their threads all appear to be tapered.

Questions:
- Will a tapered NPT thread work in our non-tapered pump-body hole? It has to seal. It looks like the NPT components are build for the seal to be made on the threads without a washer. Mismatch? Seems like this can't work.
- Is there some thread spec' other than NPT that I should be looking for, to fit in the non-tapered hole in the pump body.

Any help much appreciated.


(I'm still planning to look at modifying the stock valves in hopes of getting to a zero-cost solution. But I'd like to defer that for a bit, until we have identified one or more replacement valve candidates. Replacement valves might be a better option for many guys, and shouldn't cost much.)

 

I can't specifically speak to the specific pump and valve but I did have something similar come up umpteen years ago. On one of my old cars the metal fuel tube attached to the carburetor via a non-tapered threaded fitting. The thing kept shaking loose resulting in fuel leaks at the fitting. So I replaced the metal tube with flexible tubing and clamped on a tapered fit connection at the end of the tube. I wrapped some teflon tape around the end of the fitting and screwed it into the carburetor. Never had a problem again with leaking fuel.

Of course our case is different and the tube/fitting would be under high pressure but I suspect it should still work.

Doug

 

NPT is generally regarded as being more suited to low pressure use.

The "parker store" would likely show you some useful regulators and thread options.

Not being a ragtop owner, I have no skin in the game, but someone who should know confirmed my hypothesis to him that as p*v is involved, reducing v/t can be effective.

That is probably what the voltage reduction system does, but a restrictor orifice before the hose section(s) would be just as effective. Won't work after the hose connector though.

 

It sounds like a BSPP 1/8" thread, (British Standard Pipe Parallel). The pdf at this link gives a very good summary of how to identify a BSP thread.

http://www.pipefittingsdirect.co.uk/...tification.pdf

I would not mix parallel and tapered threads without using an appropriate adaptor but these seem to be available so I would think that's the way to go assuming the valve plus adaptor will physically fit inside the reservoir.

I drew a blank looking for a European supplier for something similar to the Kempner valves.

 

Thanks much for your inputs. Very helpful to me.

Seems I may be in for another deep dive into the wonderful world of threads. Last time was capping the hose ports for the manual latch mod. That one turned out to be ... "M12x1.5, DIN 24 degree with o-ring, 6 mm tube". Uh, right.

Looks like we're this far: NPT-tapered is off the table, as is any tapered thread. I'll look harder to see if this could be BSPP, but at first glance I'm stuck: the thread is 1/4" x 28, determined by hardware-store matching. [edit: tried to measure the threads per the BSPP spec sheet ... doesn't seem to match, but not sure yet. The OD of the thread is 0.25" by micrometer.] There is a parallel-thread counterpart to tapered NPT to look at too. And some sort of unified standard called UNF. And SAE. And ...

Will check in at the Parker Store today.


All this is making me re-think whether to just go ahead and open up one of the in-place relief valves. There is a non-zero risk of damaging it, but maybe resetting it to a different pressure will turn out to be a lot easier than stumbling around in thread-world.

 

A bit more googling suggests 1/4" UNF would fit those dimensions.

THREAD IDENTIFICATION CHART

 

Indeed it does! I went looking for adapters to get us out of the UNF thread and into a more common one. No luck so far, but just a quick try.

On the parallel effort of resetting instead of replacing the stock valves ... Bit the bullet and took one apart. Easy. Orifice, spring, ball. Going this way looks like it will take only learning a little about specifying springs. New spring -> new relief pressure. Not zero cost, but pretty close.

Pics this evening, if the creek don't rise.

 

Here we're looking at the components of the internal 1600 PSI (110 Bar) relief valve. It's about as simple as could be.

To make this an 1100 PSI valve, we need to just drop in a new spring!
[edit: that's not how they did it; see post #46 below.]

Based on the size of the hole exposed to fluid pressure, it calculates out that there is ~ 15 pounds of spring force on the ball. Spring force need to change in proportion to desired pressure change. So ... 15 pounds x (1100/1600) or ~ 10.3 pounds.

As an alternative We could make the hole bigger behind the ball. But that would not be reversible, so I don't like that option.

Anybody have experience with specifying springs? Vendors? I think we're getting close to having this all sorted out. (Still looking into a 'drop-in valve replacement' option too.)

 

Dennis
I have been carefully following your progress and have convinced fellow forum membrer Jaglenn to donate his motorless 1998 convertible top pump in the name of our Voodooo Jaguar Science proyect.

He will be shipping it to me this weekend.

I can pull the low pressure valve and send it to you so that you can test your theory on your pump and later pop the valve open to compare the innerds and spring in particular.

If interested PM your address.
JM

 

JM,

I thank you and Jaglenn both, but I'm not so brave as you imagine. All of this work is going on in a spare pump which I bought on EBay a month or so ago. (it does work, so even though its a spare I was reluctant to risk destroying one of its valves.) Opening up a valve turned out not to be risky at all.

Really too much credit to call this a theory. It's clear the measured pressures come from the stock relief valve settings. I'm just going to dial back those settings ... using replacement valves or replacement springs in the current valves.

Will be opening up an 85 Bar valve next, to see how it differs inside from the 110 Bar valve ... just a different spring is my guess.

Thanks for your interest!