Ropey wrote:

Unless the vehicle is based in a facilitated garage it should have a portable air top up unit.
This could be something that could be stowed under the stairs. A small conversion that could save lives and done carefully barely be noticeable.

If there's one thing the owners groups could do it is to look seriously into getting a portable airbooster manufactured or adapted. It might cost a couple of hundred quid but is probably more important than a spare wheel.


Would you like to expand this please Ropey

Claire

Well there's not much to expand on as it's a suggested idea.

However the motor trade aftermarket now produce a lot of devices that provide high pressure pumps for tyres etc and these are now quite compact.
The air boosters (not their correct name, I can't remember the right reference at the moment) was relatively compact but dated from a 50's design. They did require an airline in as well as one to the bus. Most in use were really antiquated.

I know nitrogen is being used but it is not terribly practical and starts to get expensive.

My guess is that a small compressor and a step up device capable of producing the required output could now be contained in roughly the size of for example a compact dishwasher.Powered by either an electric motor powered up by a vehicle of from mains.

As I said, it's an idea, but a remote stored vehicle with sub-safety brakes is a bigger problem.

Hiya Ropey

That seems a good idea but the nuts and bolts are a bit beyond my expertise.

So a small compressor that would say normally be used for pumping up the tyres could be connected to a 'step-up' device which would then convert the probable 100 psi from the small compressor into a higher pressure (how higher?) to then allow the brake accumulators to be pumped up to a suitable pressure (what's suitable?) for use.

My understanding of the system is that it's a hydraulic one and the accumulators are there as a kind of belt and braces to ensure that if the hydraulics fail the braking system will still work because of the hydraulic charge held in the accumulators and not usually used in everyday stopping, and the accumulators would be kept at a suitable pressure by the occasional air charge from a high pressure air line from off bus.

In other words the charged accumulator does nothing unless there is a hydraulic failure and then it automatically comes into play provided it has enough pressure in it.

Am I on the right lines??

Claire

I don't want to question Ropey's wisdom in the slightest because I am in awe of his knowledge and experience, and I'm quite prepared to have my comments shot down, but it does seem to me that the nitrogen solution might be preferable because (a) it doesn't need a power supply (b) the gas is inert so there should be no, or less, corrosion in the accumulators and (c) it's comparatively readily available. One drawback, as Ropey says, can be cost but the mini dishwasher sized machine doesn't sound especially cheap either.

My accumulators have been pumped up on numerous occasions with argon. This comes in a tall (about 5 feet)and thin cylinder which is very scary to use because of the prospect of it falling over and spraying shrapnel. I did however see some propane cylinders in B & Q the other day which were squat and much easier to handle and wondered if it was possible to get nitrogen in something roughly that size?

Whatever method is used however I quite agree that safe brakes are an essential matter that every owner must address.

Thanks for the compliment, my head is now to big to pass through the cab window!!

The nitrogen method is a superb solution but is going to become more expensive and heavy restrictions are in the pipeline for storage and use of all gas bottles as a result of the spate of incidents over the last few years.
This is aimed at flammable gases such as acetelyne, but because of the similarity of all storage bottles, Oxygen and cooling non explosive gases will be subject to these new restrictions
So long term, portable air may be a better bet for the average preservationist/user.

I'm no expert on compressors and the like and not expert on the nuances of RM brakes. But I have experienced low brakes and dropping flags on RM that have no detectable problem with their brakes and this has been rectified simply by topping the accumulators.

What I do know is that an RM should not be driven or moved without a sufficient reserve of air and if low moved with extreme caution.

I understand from engineers that the RM compressor cannot fully charge the accumulators from below 80% charged.
but that in continuous daily use the reserves did not drop down. There was always the odd bus that would need to go on the pit every few days and baffle everyone as to why it needs topping up when nothing wrong could be found in the entire system.
RMA10 at Mortlake, The staff bus was notorious for this and it did long runs. Just about everything was replaced and still drivers complained and that was with the standards that made Mortlake legendary.

A device that might cost a few hundred quid could be shared by some who keep buses together but would be useful for those in remote places where gas storage may become prohibited.

Ah.....I should have known there was a good reason for the suggestion!!! Thanks Ropey! I think Roy might have speculated about this before too - I wonder if it would be feasible to have just the booster part onboard so that a garage air line or as Claire says one of those little electric pumps could be connected to a valve on the bus when necessary?

... there are some likely-looking machines @ http://www.pneu-store.co.uk/acatalog/Pressure_Boosters.html but I'm not really sure if they are what we are thinking of...

Yes agreed, It would need someone who knows all about this domain to lay down a specification and then to see what is available.
It could be as simple as a plug in point hidden somewhere around the bus and powered by a remote compressor such as a garaged airline or portable compressor.
a relatively simple mod could stow this under the stairs.
I saw a mod once that in which part of the steps lifted up and out but when in situ you simply would have no idea.
clever stuff.

The RM brake pumpup unit is called an ' Intensifier ' and is nothing more than a unit for ' drying the air ' before passing it into the Accumulators . It is this dried air that has been the reason that accumulators lasted so long on buses in service . The dried air did not have any moistiure content at all therefore the accumulators were kept very dry internally with no fear of corrosion , the only real way for failure was if a minute piece of dirt / grit was to get thro' the schrader valve and into the Acc's this would then eventually get trapped in the seal between the hydraulics / pneumatics and lead to leakage ..

There was a company in the Newcastle area many years ago that could make NEW intensifiers ..costs of £6,000 +++ were quoted even back then

Colin Curtis called the intensifiers ..PUFF PUFF machines ...