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Boiler Fittings

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Matt Stevens 125/06/2020 03:05:21
97 forum posts
11 photos

Hi All,

I am going to ask some simple questions, but they are important since i am picking threads for bushes on my model boiler.

I am making the Reeves 6" vertical boiler and so its abit of a beast, but should be good to run any models in the future. What i am trying to work out is the requirements for the fittings....for example....

- Water Gauge. Is a plain one with a drain cock sufficient or should i get a 3-cock type which are much more expensive? If so why? Is 6mm glass sufficient (means a 5/16"x32 bushes)

- Blow down valve. Is bigger better? i.e. 3/8"x32 bush?

- Check/clack valves. What are they for? I understand these have a spring loaded one way valve inside correct....are these for water injection? How many should a boiler have? Again is bigger better? (3/8" x 32 bush)

- Steam take off. The drawing calls for a 5/8"x26 external thread but i can't understand what/how you would connect to this. I can imagine more an internal thread of 3/8" x 32 going to a globe valve. Any thoughts?

- What size piping would you generally expect for a boiler this size? 3/16" or 1/4"? Would the answer differ between check valves and take off?

- Injectors. What are these for? I am confused between check valves and injectors for boiler filling.

In total i can see 1x take off, 1x blow down, 1x blower valve, 1x safety valve, 1x water gauge, 1x check valve. Have i missed anything?

Finally - i see a big difference in pricing for fittings between different vendors. Best i seem to find is GLR Kennions or Blackgates. Are these the recommended suppliers for what i need? I will be shipping to Canada so one vendor for everything is ideal.

Many Thanks


Paul Lousick25/06/2020 05:44:47
1901 forum posts
673 photos

Hi Matt, I will try to answer a few of your questions but not familiar with a Reeves 6"

Firstly, are you building to a drawing because all of the sizes should be on it ? I would also suggest that you find a model club in your area before you undertake a big project and are unsure about anything.

3-cock water gauges allow you to test if it is working correctly and check and clear any blockages in the steam and water ports. If the glass breaks, you can turn off the water and steam to the glass. And replace a glass with the boiler still in steam.

A 6mm glass (or slightly smaller) should be OK. My engine has a 10" boiler and I use a 5/16" (8mm) glass.

3/8*" Blow down valve OK. Water is under pressure and you do not want to empty the boiler too quickly.

A clack valve is boiler slang for a check or one way valve and use on the water inlet to the boiler to prevent the back flow of water and steam. The valve stem inside the valve is normally mounted in a viertical direction and is closed by gravity. A spring is not normally used to close it. Stainless steel ball bearings are somtimes used instead of a stem to seal the valves on small models.

Most boilers have a sockets with a female thread, not male and should be steel for a steel boiler and bronze for a bronze boiler. (do not use brass on a bronze boiler because they can corode)

Injectors are a ventury type device that is used to fill the boiler with water, using steam from the boiler (do a Google search). Both injectors and a water pump have a check/clack valve between it and where it enters the boiler.

Good luck, Paul


Edited By Paul Lousick on 25/06/2020 05:47:34

JasonB25/06/2020 07:24:35
22017 forum posts
2540 photos
1 articles

On that size boiler I would suggest two clacks as a means of getting water into the boiler so the level can be maintained while in steam, one connected to a hand pump and the other could be to a pump on the engine or possibly an injector though they are less common on stationary setups.

Pipe sizes will really depend on what you are running, a 10V won't need the volume of steam that say a Swan will.

There is a very good build thread of the RV6 over on MEM forum, you will just need to sign up a sthe photos are posted as attachments so have to be a member to see them

IanT25/06/2020 09:09:50
1946 forum posts
194 photos

I have used Blackgates for many years Matt - buying mostly at shows but also by post. I've never had a problem and the quality has always been good. I've not used GLR Kennions (that I can recall) but I have no reason to doubt them, as they've also been around for a long time.



Matt Stevens 125/06/2020 21:01:47
97 forum posts
11 photos

Thanks for the comments everyone.....

So i understand i will not feed an injector then on my setup? .....2x clack valves as Jason suggests is probably a better alternative. I have made a Stuart steam pump and a hand pump to complement that could be a good idea.

Pipe sizes - Well i will be running a twin Victoria, a Triple (when i make it) and likely others in the future like a major beam or something. Perhaps i should assume 1/4" piping with those models in mind?

@Paul - You asked about the drawing and what it calls for....well it gives the option for either 3/8" or 5/16". So for example, that would dictate the size of the water gauge and hence the cost of the water gauge. This is why i asked if 6mm is sufficient as that would point to the 5/16"x 32 bush.

I will try to post a few pictures later for interest purposes....

Matt Stevens 125/06/2020 22:31:26
97 forum posts
11 photos

boiler 2.jpgboiler 1.jpg

JasonB26/06/2020 07:03:05
22017 forum posts
2540 photos
1 articles

Stuarts list 1/4" supply for the twin Victoria and 5/16" for the Triple, No4 and No9 are 3/8" probably best to fit something that will work for the largest dia and then adapt down for the smaller engines. These pipe sizes are if you want the engine to do something, just ticking over on display could be a bit smaller.

Edited By JasonB on 26/06/2020 07:05:02

Matt Stevens 126/06/2020 13:31:38
97 forum posts
11 photos

Thanks Jason.... The design has a twin superheater, each using 1/4" pipe (thick walled). I would have to double check the inner diameter of the superheater pipes, but i guess that also sets a limit in that the volume of steam that can be delivered.

Nigel Graham 227/06/2020 00:31:49
1898 forum posts
26 photos

I don't know the individual design but a super-heater should not act as a restrictor as I think you fear it will, because it normally has two or more elements working in parallel.

I think you can trust the boiler's designer to have matched the superheater to the intended maximum steam-pipe size.

As a rough guide, two tubes of 1/8-inch bore have a combined cross-sectional area almost equal to that of one tube of 3/16-inch bore.

' ' '

It is usual on a model boiler to have two independent water-feeds, each with its own clack (or check) valve. Typically one is a hand-pump; the other either an injector or a mechanical pump. The latter can be driven directly by the engine itself, or is a separate Weir-type unit.

Injectors were sometimes used on full-size boilers in factories etc., where the engine was in a different room to the boiler, or the steam was for process-heating rather than powering an engine.

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