Where is the water going?

[Michael CallaghanParticipant @michaelcallaghan68621]

Hi. I have a bit of a mystery on my hands. Today I tried to do a bit of hydraulic testing on my butch locomotive, just to make sure that the fittings are ok etc. however when I put water pressure into the boiler in this case 75psi, the pressure holds and then goes down to zero again. I have the loco  on stands so I can see underneath and have laid out cardboard underneath to indicate if there is a water leak. I can see no leaks. The fittings are holding, the firebox is bone dry and so is the smoke box. The locomotives own pressure gauge is reading 40psi, and the gauge glass is showing full. I can’t see any blow back into the water reservoir of the cheap Chinese pump I am using.

can anyone please put some light on this. Any sensible suggestions. Thanks.

[BazyleParticipant @bazyle]

Well my first thought was back through the pump but you thought so too. Perhaps it is the last bit of air and possibly then water going past the regulator and filling the superheater and cylinders.

The volume of water to drop the pressure will be miniscule.

[SillyOldDufferModerator @sillyoldduffer]

Once the boiler is full of incompressible water, the pressure test doesn’t put any more water in, or at least very little.   All that happens is force from the pump handle increases the pressure inside the boiler, which the pressure gauge registers.

I guess the pump valve is leaking slightly, allowing the pressure to release back through the pump.  No blow-back seen because the amount of water is tiny.   Or possibly the boiler is weeping somewhere inaccessible, and the tiny amount of water released won’t become visible unless the pump keeps the pressure up for a long time.

Pressuring the boiler with an incompressible liquid like water is far safer than testing with air, or even worse steam.  Air is compressible, so every stroke of the pump not only raises the pressure, but stores energy in the air as if it were a giant spring.  If an air-pressured boiler breaks, a lot of energy is released with a bang.  Steam is far worse because it contains a lot of heat energy as well.

Hydraulic testing only puts the energy of the last pump stroke into the boiler – far less, and very little of it is stored.

Dave

[Speedy Builder5Participant @speedybuilder5]

I guess there is still air in the boiler and associated attachments. Leak back through the pump ??

[Speedy Builder5Participant @speedybuilder5]

If you are using the loco’s pump, the leak back would go into the side tanks ??

[noel shelleyParticipant @noelshelley55608]

The regulator is not sealing well enough and the small amount of water is filling the cylinders, super heaters Etc. When all this is full it will hold or start to leak – somewhere. OR, your cheap chinese pump is leaking back. Try fitting a stop valve between the pump and boiler, open valve, pump up and then shut. If the pressure drops its the boiler Etc My Rothenberger proof pump has valves for this very reason. Noel.

[Nigel Graham 2Participant @nigelgraham2]

Of various leaks on my tank loco when similarly testing it recently, one of the most subtle was via the axle-pump feed-check valve and the bypass valve, to the point I could release the pressure by opening that.

A leaking regulator’s main symptom, apart from falling pressure, is water dripping from the cylinder drain-cocks.

Air alone won’t reduce the pressure. It will compress as you pump water in, so you need pump more water in, but the air and water pressure will equate. The reason for removing as much air as possible first is safety, as SOD describes.

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