horizontal boiler stays

I recently acquired what is in many respects quite a well built horizontal 'marine' type boiler. It has the normal centre flue and cross tubes. It looks to be almost finished but unused.

Everything is silver soldered except for the two longitudinal stays which have copper washers under bronze fittings each end. At one end of the stays the bronze fitting has spanner flats and of course can be unscrewed. All of this has been in place for a long time and sat on a shelf by the look of it.

I would have thought the stays would seal better if silver soldered?

Though I see a few articles about comsol? or even using loctite on threaded stays to caulk/seal.

Any recommendations on how to seal these, or should I silver solder them? of should give it a good pickle and loctite I leave them?

Cheers

WHY were they not soldered when it was built ? I would start by relying on annealed copper washers, this keeps your options open, silver solder is rather permanent. Loctite may fail at elevated temperatures, or even try Boss white and Hemp. Noel.

Some people think as you do and others consider silver soldering to be less safe as the stay may not be under tension if not straight or expand on heating and crack the joints on cooling.

I make no claims for which is best only that I have seen all viewpoints expressed in the past.

make up a fitting to suit a bicycle pump and give it a whiff of air (only a few psi so it's safe) so you can see if it leaks. If not leave well alone. Silver soldering of end to end longitudinal stays is not allowed in the AMBSC code for the reasons Nick outlined. If it does leak it rather depends on exactly how the stays are screwed into the end plates, photo would help. If you are tempted to silver solder then heat the whole thing and allow time for the stays to reach the same temperature as the shell

Thanks for the advice. So you are saying its fine for the stays to be screwed.

I'll have to try pressure test. Will have to play with how much torque to give them.Though internal pressure will i expect tighten against them. Under heat they will expand in length regardless of if soldered or not. Also seem to see many that do have soldered stays. But if this works like it is thats fine.

The stay is only screwed one end and long 'bolt' with head and other end (see images), copper washers underneath at each end. So basically they have a flat nut threaded internally one end, and 'bolt' head the other end.

cheers

Those stays are so close to the central tube that they won't be doing a right lot. If it doesn't leak it's fine, if it does I'd try various sealants before soft or silver solder. Without any sizes/dimensions it's hard to tell what working pressure it is good for

The stays will get longer as they get warm, but so will the shell, and deflection due to pressure will tend to keep the stays in tension

Those stays are so close to the central tube that they won't be doing a right lot. If it doesn't leak it's fine, if it does I'd try various sealants before soft or silver solder. Without any sizes/dimensions it's hard to tell what working pressure it is good for

The stays will get longer as they get warm, but so will the shell, and deflection due to pressure will tend to keep the stays in tension

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Thank you all for your thoughts and advice. will start first with some air and see what happens

for those interested, the boiler and stays hold air quite well. one fitting was more an issue getting sealed than the stays which were no problem at all.

Screwed ends on stays are common on full size boilers. Some have thicker tubes with screwed ends instead of solid stays. Tubes are normally expanded with a special roller to seal them into the end plates.

Pressure testing of a boiler should not be done with air.

Water should be used in case there a problem. It the boiler ruptures there could be an explosion as the compressed air expands. Water on the otherhand does not compress like air and the pressure is quickly repeased without a big bang. (If you must use air pressure because you don't have a pump, fill the boiler with water to reduce the volume of air inside of the bolier).

Paul

Mains water pressure in most areas is at least 60psi, at my mates out in the sticks we measured it at 120, so just connecting to a hose is an option.

Paul.

thanks, well aware of the risks of using air. Will try the hydraulic pressure test once I have a pump and a valve and a few bits to connect it.

Mains pressure as Paul suggests may be an option - at least for a low pressure test.

cheers

My mains is 1.8 bar - so not much of a test. Yours might be different.

not a problem using air at a few psi to find leaks.

I did once have to pressure test a vessel which on no account was allowed to have liquid inside it ever. We found out which safety guy had a practical head, and pumped it up with air with the vessel and compressor in an old air raid shelter. It was only a small vessel, and not very high pressure. It was a containment for an induction heating coil which the boffins wanted to run at more than atmospheric pressure. Apparently it is less likely to arc, counter-intuitive really. The vessel was made from UHMWP, again not a material you'd normally choose, but it has very good insulation properties I'm told.

.

Not disputing your numbers, Paul ... but I’m surprised

To my limited understanding: [in the UK] there is currently no legal maximum for pressure ... but your numbers do seem unusually high.

MichaelG.

.

**LINK**

https://www.watersafe.org.uk/advice/common_plumbing_questions1/pressure/what_is_the_minimum_water_pressure_that_a_water_supplier_must_supply/

**LINK**

https://www.southwestwater.co.uk/frequently-asked-questions/drinking-water-services/what-standards-apply-to-water-pressure/

**LINK**

https://www.affinitywater.co.uk/my-water/water-pressure/high-pressure

We live in an area with a lot of dairy farms (South Cheshire) and I understand the water pressure is high because the farms use a lot of water. We had to install a pressure reducing valve to reduce it to 3 bar as it was causing us problems. There are also a high number of water leaks in the distribution system that need to be repaired because of this.

Richard

The other problem with pressure testing with air and is one why you shouldn't do it is that is there is a leak with air the pressure stays high, very slow reduction, so is the vessel ok or is it leaking or is the leak outside the vessel from the pump or connections/pipes. With water with every drop that leaks out the pressure rockets down, so a far more positive test. Plus it's easier to find a water leak than an air leak.

Around here water pressure can be 80 PSI. I have seen a steam boiler in a lumber yard used for steaming timber at low to moderate pressure that was hooked to the mains water supply, directly through a check valve, so feed water relied solely on mains water pressure. The operator had a valve on the feed line he adjusted to match flow to water level in the boiler. Probably not strictly legal I should think. The boiler ran at a lower pressure than the water mains so it worked though.

I've even seen two-story houses fitted with a disability lift powered by water pressure from the mains. The water operated a large ram like a hydraulic ram set into a deep hole in the ground. Enough power to lift a steel platform and cage carrying two people and a wheelchair up to the upstairs floor. Also no longer legal but still a few in operation out the back of old timers' high-set houses in small towns. Horrendously dangerous with no safety interlocks etc in the hands of ageing operators and resulted in at least one death I know of. They used to be installed by local charity service clubs like Lions and Rotary etc.

Edited By Hopper on 19/05/2021 11:32:36

Edited By Hopper on 19/05/2021 11:34:58