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| CCairns |
Mamod Pressure GaugeJust wondering if anyone has tried the Mamod Pressure Gauge that is available from Forest Classics ( http://www.forest-classics.co.uk/pressuregauge.htm and http://www.forest-classics.co.uk/pressureadapter.htm ) and other dealers?It is a 30PSI gauge which is fitted using an adapter. However this adapter is a simple straight through design, and thus the gauge is not protected by a syphon tube. This I believe leads to some over-reading indications ( I have one fitted to an SP6 which I've just bought and it indicates about 24PSI when the engine is running and Safety Valve has barely lifted ), and also allows the steam to condense inside the gauge, which will lead to corrosion. A syphon tube should be fitted so that the steam condenses providing a water barrier, and thus the gauge is not feed direct steam. If I can get the body of a safety valve I will fit this gauge with a proper syphon tube and see how this changes the pressure indications. Chris Cairns. |
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| tmuir |
Excuse my ignorance here Chris, I get what you are saying but don't understand how a siphon tube works.
Could you post an explanation or picture to help the not so enlightened people like me? |
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| Reid |
I've seen pictures of proper model engines whose gauge is fitted with a siphon tube, a U under the gauge instead of a straight connection.
I wonder how the Wilesco gauge is made, that it does not need a siphon tube? Or is it the same deal as the Mamod gauge? |
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| CCairns |
Hi Tony, Sorry no pictures possible at present, but if you look here you will see the syphon tubes and pressure gauges - ( http://www.stuartmodels.com/acces...type/6/the_type/Boiler%20Fittings )
I am just going by what I read previously on the internet, that apparently some of the steam condenses in the 'U' part of the syphon tube and prevents wet steam from entering the pressure gauge - a bit like the 'U' bend in a sink drain (well at least that's what we have here in the UK). Hope this makes it a bit clearer. Chris Cairns. |
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| Mister Occlusion |
Wondered about those tubes myself. Jensen uses a standard off the shelf gauge of some sort that goes on through a simple thread adapter as well.
The literature for the gauge makes no mention of using a siphon tube in any of the applications that they rate it for. Could be these things don't need them, on this scale. SVs are not that reliable either IMO. I have used the same pressure gauge on many boilers with several different SVs made by Jensen in the last 40 years. If anything I see a trend where modern ones let off at 15-20PSI (indicated), and the older ones more like 25-30+ (gauge tops at 30). Needless to say I keep all of the older ones that I can find 
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| Nick |
When the safety valve lets off, what is it like? I have never let my engines build enough pressure for it to happen. Does it just slowly lift and leak a little steam, or is at an instant release of steam? | ||
| johnreid |
Mine seem to bubble a bit then become a bit more steady. From my experience there is a cycle as such: fill boiler to proper level and apply heat, as pressure begins to build some of my Safety Valves like to bubble a little bit as I suppose things are expanding, the bubbling stops at the SV and the regulator or cylinder begins to bubble or hiss, as the pressure builds up more the Safety Valve begins to spit a bit of steam, if one allows it to happen steady steam comes from the Safety Valve.
I am finding that on my electric Jensens, that when the Safety Valve begins to want to spit a little it is time to run the engine for a nice long run, for my Meths and Esbit fired engines, I am way too impatient to wait that long, I let them run as soon as there is enough pressure to let them run. If there is a speed control as with my SE2, I run at low speed for a while before running all out as pressure does seem to continue to build when running a slower speeds. IMHO it is all where you are the most comfortable, I do not like to wait till the Safety Valve actually pops off and that has only happened to me once when the stupid phone rang while I was first plugged in and drew my attention away from the engine. However I got a good 20 minute run after that. |
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| tmuir |
All Mamod and Jensen and most other toy valves release as John says, a few small hisses and bubles that gets faster as the pressure builds up but you can also get 'Pop' safety valves that stay closed until the presure is reach and then 'pop' open and release more steam at once. They look better releasing the steam and make a nice 'pop' when they open but just don't be leaning over them when it happens. Roundhouse uses pop safety valves. |
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| johnreid |
In a manner of speaking the Pop Safety Valves are not as Safe for the very reason you said, it is way too easy to get your face or hands too close to an engine when messing with it. | ||
| Mister Occlusion |
mine will hiss or bubble. At some point they will suddenly let go and a fan of steam will jet from one side or the other.
I never let mine blow off either until I got a pressure gauge and saw how low the pressure actually was. Mind you, I'm still more comfy letting a Jensen blow off than I am with a Wilesco. |
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| CCairns |
The standard Mamod Safety valves release the steam sidewards, whereas the upgraded safety valves made for the Mamod locos release steam upwards, which is more in keeping with the real world.
I have one that is a pop valve like Tony describes, and when it goes off it is like having sprung a leak on a high pressure water line - stand well back!! Still not had any feedback to these Mamod Pressure gauges which was the topic of this posting originally. Chris Cairns. |
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| Mamodman123 |
I've considered putting a Pressure gauge on my loco, but i've never had any experances with them 
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| steamyjim |
I put one on the manifold my grandad made me for my upgraded Mamod loco I used a syphon beacuse it stops the water condensing in the pressure gauge
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| CCairns |
steamyjim - And did it give a good indication Jim, as the uprated safety valve should work between 20 and 25 PSI depending on how it is adjusted? Would like to see a photo of it fitted with your syphon tube if possible?
Interestingly I've just tried fitting a standard Mamod safety valve to my SP6 and the gauge indicated a lower operating pressure than when fitted with the supplied safety valve, which like the one supplied with the 'William', has a more compressed spring - thus should operate at a higher pressure. Chris Cairns. |
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| steamyjim |
Ill try and get a pic of it soon. The paint on the bodywork is currently curing. Then i can start assembling it ready for STIA. Then take it apart and finish it off after that 
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