Choice of mechanical lubricator

Hi folks,

What thoughts do people have about mechanical lubricators for 3 1/2" gauge? LBSC's is well tested, but some complain about it issuing too much oil. Martin Evans did one for Rob Roy which I have good things about. Both have been taken on into new loco designs, but what others are liked?

Dave

Very small lubricators need excellent workmanship to work reliably. I sleeved down the LBSC one on my Juliet-sized 0-4-0ST and had a lot of trouble in getting it to deliver oil at all - I was using a 1/16" diameter ram, and it needed the mating surfaces to be almost mirror finish and really well-fitting, or the oil just squirted past the ram. (One idea I had but never actually tried was to use a tiny O ring - pull an old disposable fag lighter apart and see what you find!)

Having said that, the Jim Ewins design is pretty straightforward. I've got a pair of them on Edward Thomas (admittedly that's 5" Narrow gauge) but hiding one unobtrusively between the frames should be possible. The Jim Ewins design has the advantage that oil delivery can be reduced to very tiny amounts to suit your needs. If I needed a new pump for Tiny, I'd probably make one to the Ewins design.

I'm surprised no one has tried other tpes of pump in this application. A diaphragm pump like a miniature car fuel pump should be leak-free. A peristaltic pump (as used for measured drug delivery) could deliver even the tiniest quantities of oil with complete reliability. The simplest could be one based on a cylinder with a piston that screws in like those used for morphine - more bother to refil when empty, but again tiny quantities very reliably.

Neil

Neil - interesting ideas; I don't know much about these techniques; do you have any practical solutions for these applications?

Hi Robert,

I was just thinking aloud.

A peristaltic pump here could be made with small bore tubing quite easily. The only tricky bit would be making the roller/housing clearance just right. Silicone tubing that has plenty of 'squash' past the closed tube point might be suitable.

With a diaphragm pump the challenge would be making a suitable check valve to allow it to administer small enough quantities reliably. On reflection for releiability I would go with a peristaltic design as it's simpler than the usual oscillator design (i.e. it's valvless) and could be made inside the same oilbox and use the same ratchet drive. I'd use two or three small ball races as the rollers.

Neil

Please can someone tell us where and when details of the Jim Ewins lubricator design was published? (Unless there is a problem as it may be the other magazine?)

It's in the other mag Vol 4 No 2, Jim did not write a great amount in ME. Ian S C

Neil,

thanks for the explanation. However the problem I see with this idea is that, like all our lubricators, it has to operate at steam pressure and so soft flexible tubing would not work, unless the whole thing is pressurised which adds to the complication.

Fair point Robert, although 1/8" silicone tubing seems to take 30psi OK, there may be some types that would do the job. Your pressurising idea sounds interesting, but as you say it could be more, not less, complicated!

Neil

Just a word of warning! When you decide what type of lubricator to make you have to decide if it is a single or double. If your oil feed is by means of one pipe into a header or similar the a single pump is fine, but if your feed is to two places i.e. valve chests then you will need a twin pump. The reason is that it is virtually impossible to get two delivery valves to open at the same pressure. Oil like any other substance will find the line of least resistance and go through the delivery valve that is weakest, the other cylinder will get none. It may seem a lot of work making a second pump but beleive me the time is nothing comared to the time spent faffing about over the years trying to get your oil feed right. You will end up making a twin pump anyway.

Remember that a lot of models were designed with no pump at all - relaying on saturated steam as the lubricant with just a drop or two added to the steam chest before a run.

Hi Robert,

The medics obviously have need for more robust tube than we expect - it seems that 1/8" bore silicon tubing for use in pump applications is available with a working pressure of 170psi and a burst pressure of 680 psi. With a minimum radius of under an inch, I would have thought this would be ideal.

Here's another that is 1/16" bore and 200psi working pressure.

Another one claims "At a back pressure of 4 bar (60psi), this pump tube lasts over 1,000 hours with continuous use at 200rpm in a Watson-Marlow Bredel 700series pump. Under transfer conditions, it exhibits 18 times the life of silicone rubber tubing, and nearly twice the life of thermoplastic elastomer tubing with continuous pumping at 360rpm. The risk of premature tube rupture is significantly reduced"

200 rpm is far more than we would need, but it would also be easy to fit multiple tubes within teh same housing/roller arrangement.

Neil

Neil, could be an interesting project, but getting hold of the tube and designing the pump would be a challenge for most people.

In practice a displacement lubricator is the simplest and most effective solution.

My 3.5" Netta had a commercial lubricator fitted which used up the whole lot in under an hour (and deposited it all over me), this had a 1/8 ram, so I sleeved it and inserted a 3/32 piston which works very well. It still seals with a top nut and packing as it did previously, without having had to do much changing.

del.