pneumatic fittings

[michael howarth 1Participant @michaelhowarth1]

can they be used for LPG

[michael howarth 1Participant @michaelhowarth1]

I have used 4mm pneumatic push fittings for loco plumbing for a while now and find them to be cheap, reliable, unobtrusive and easy to connect/disconnect. Typical specs are up to 60 deg.C use and 10 Bar pressure and for use with water, oil and air. There is a really neat little flow controller in the range that I would like to use as a butane gas controller but I cannot find out whether it is suitable for LPG. The suppliers are very cagey about recommending them for this use and I don't blame them for not committing themselves to something not specifically mentioned by the manufacturers. But, I am also aware that things can be used quite safely for purposes not specifically recommended eg if water is OK, what about beer?

My experiments so far have been quite satisfactory but are there any experts out there with a point of view?

Mick

[geoff walker 1Participant @geoffwalker1]

Hi mick,

How about some more information? photos, suppliers.

[Martin ConnellyParticipant @martinconnelly55370]

If you get a leak of water, oil or air from these fittings there is either an obvious leak with the liquids or no hazard from the air. Using a flammable gas if you get a leak there is no visible sign and a risk of a gas buildup with a potentially explosive mix ratio. Does not sound like a good idea to me.

Martin C

[michael howarth 1Participant @michaelhowarth1]

Hallo Martin. I take your point but a gas leak from any fitting will be equally not detectable. It will still go bang (under the right conditions) whichever (faulty) fitting I use.

Photo of the flow control on way.

Mick

[JasonBModerator @jasonb]

Sounds like you want to use these. They are nice valves and give a very fine control of flow though I have only ever seen them sold as suitable for inert gasses

[michael howarth 1Participant @michaelhowarth1]

[michael howarth 1Participant @michaelhowarth1]

Jason…..yes spot on (and a better photograph than mine). They do offer very good control as you say and seem to be very well made. The body of the controller is nylon. I seem to recall reading somewhere that the reason that some controllers fail is because of the molecular size of the substance that is to be controlled ie the smaller molecules squeeze past, but LPG gases are generally, I believe, heavier than say Helium and I don't think that this would be relevant here.

Mick

Edited By mick H on 05/11/2018 16:12:56

[David George 1Participant @davidgeorge1]

Hi Mick I personally wouldn't risk as the pressure in a gas line could leak with catastrophic results when a proper gas connector costs so little. see item listed others available.

eBay item number:

371661376748

David

[michael howarth 1Participant @michaelhowarth1]

Thank you for your interest David. The vapour pressure of butane at 25 degC is only about 35psi. The controller is rated at 10 bar so there is a pretty significant safety margin.

I have had a look at the Ebay item you mentioned but that is for a full scale appliance. What I need are gas controls for small scale …..typically 10mm to the foot ….locomotives, traction engines etc. My current build is a launch with a steam/gas propulsion system. Cost is not a problem but because miniature gas controls are not generally available I invariably have to design and make my own. The controllers that I am referring to are far superior in control terms to anything that I have been able to make in the past.

Mick

[martin perman 1Participant @martinperman1]

Where I worked as a service engineer we used them and as you say they are excellent flow controls but they do suffer from chemical leaks and will become brittle, we replaced them with the same make but metal ones.

Martin P

[JasonBModerator @jasonb]

David, having used the regulators shown I would be happier with the gas tightness of the push fits over those any day.

 

Having said that the e-bay can regulators are no bigger than the others and can give fine control too. M7 x 0.75 thread if you do buy one

And controlling the gas on a small model or two

 

 

 

Edited By JasonB on 05/11/2018 16:53:18

[michael howarth 1Participant @michaelhowarth1]

I have managed to establish that these things are not manufactured in UK but I have a couple of contact leads to pursue in the morning.

Mick

[SillyOldDufferModerator @sillyoldduffer]

As we don't know what the flow controller is made of, it's impossible to say. Assuming it's Nylon, then this site gives Nylon and Butane an "A²-Excellent rating". Sounds good, but the A² footnote means up to 22C, ie room temperature. Presumably Butane starts degrading Nylon at higher temperatures.

More worrying is what else might be in the gas? For example an impurity like Benzol would have a severe effect on Nylon and cause an early failure.

When you buy a reputable product intended for a particular use the maker will have engineered it properly – material compatibility issues will have been checked out by experts. In this case, that hasn't been done. My guess is it would be fine, but I wouldn't risk it if a leak could have consequences. That depends on use – boats used to be blown up regularly by minor leaks because heavier than air butane sinks inside the hull and can't escape : their situation was far more dangerous than the same tiny leak in a caravan.

Dave

[michael howarth 1Participant @michaelhowarth1]

Thank you Dave. That is the sort of information that I need. I am quite happy about the push fit seal but possible degradation of the body is an obvious concern. I have been told that all metal versions are available which should solve that problem and I hope to discover where I can get them tomorrow. The link that you posted is a really useful one.

Mick

Edited By mick H on 05/11/2018 20:19:16

[martin perman 1Participant @martinperman1]

go to your local pneumatics supplier and they will have what you need, RS stock plastic and metal parts.

martin p

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