Help with water pump - no pressure

[NP317]

Well presented info, guys!
RussN

[Charles T. McCullough]

Like this:

LocoTenderPlumbing.jpg

Showoff.

I drew that many (too many) years ago for an article in SitG magazine... but now I can't remember if I ever sent it in to be published!

[Glenn Brooks]

Yes, well presented.

Good idea to add a hand pump. I don’t have one, probably should get one. Priming the axle pump would be my primary usage.

Although thinking about it, I suppose one could plumb a branch line off one of the injectors - inject water into the axle pump as needed without adding an expensive hand pump. Hmmm.

[Bill Shields]

Always put the hand pump through the axle pump...helps free stuch checks.

You can also use the Purinton trick or throttling the feed line and having no return.
Just sleeve or notch the feed valve so that it cannot ever be fully closed.

Works a charm and reduces components.

[Glenn Brooks]

That is called a surge chamber. It's exactly what you said: An air cushion for eliminating huge pressure spikes when running the pump at high speeds, since water is incompressible. Not really needed on anything the size we are dealing with. If you get your piping and check valves where they flow good enough to handle the full output of the pump easily, then there won't be any problems with huge pressure spikes.

Iam still intrigued by the idea of a surge chamber. I could maybe add a surge chamber made out of out of 1” pipe fittings and 2” nipples, in-line right at the location where the water pump pressurizes the inflow from the tender. This would give me a volumetric area of 4” x1” ID as a surge chamber. Or could machine one out of some 3” brass round stock in sitting in my rems bin.. Then step back down to normal 1/4 or 3/8” or whatever it is going into the boiler. Would this be a good idea or a bad one? Wondering about disrupting water flow coming out of the pump??


Once again, wondering if great ideas and successful operation are running in opposite directions here.

Thanks,
Glenn

[Harold_V]

How would you prevent the surge chamber to which you refer from filling with water? Once filled, it is no longer a surge chamber.

H

[Charles T. McCullough]

Look at most of the steam powered fire engines and you'll see a large globe thing on top of the pump.

th-4158374634.jpg (37.24 KiB) Viewed 1264 times

That copper globe near the front is the surge suppressor.

It needs a valve on the top and bottom so that it can be drained of water that will eventually fill it in use. The water surge from the pump compression stroke compresses the air as water surges into the chamber and the air will eventually be entrained in the water over time (the higher the pressure the quicker the air is removed with the water -- like carbonating a beverage!). It is also like a household "water hammer suppressor", except they often have a rubber membrane in them dividing the air and water portions of the chamber and they don't need drained, though sometimes the water needs to be shut off to remove pressure in the water half and a valve in the top opened to let the membrane equalize the two chambers.

[Glenn Brooks]

Thanks Charles. Truly I have learned some new things today!

I know my original concern is to ameliorate pressure spikes, and mitigate risk of blowing out a fitting. The surge chamber idea probably will be difficult to implement given the limited space I have available between the boiler and the running gear. It’s a Complicated undertaking also. Right now I think I will make a simple plenum to mount the pump intake, return tube and the injector line and somewhere in there install a smsll inline pressure relief valve simply to relieve any unwanted 250 psi pressure spikes.

[Fender]

Surge chambers, aka “water hammer arrestors” can be bought from the big box stores such as Home Depot. Or, make one from an empty CO2 cartridge. The dome end has to be pointed up.

[Bill Shields]

Stop and think for a minute

Isn't a boiler full of water and steam a very large surge suppressor by definition?

I think you are looking for a solution to a problem that does not exist.

A surge suppressor on a fire hose discharge that can be shut off and or needs to be controlled is one thing...dumping into a boiler is another.

[Charles T. McCullough]

You are correct that you are feeding a boiler, so as long as the clack-valve is not stuck closed then the boiler acts as a surge suppressor. But on a fire truck, the hose can be open but not allowing full flow from the pump, but even then you can still get too much pressure in the system as you continue to compress the air in the surge suppressor (same is true with the boiler, if the safeties get stuck too!). The fire truck surge suppressor moderates the pressure so the hose does not pulse and the firemen does not get knocked backward on each pump cycle and then fall forward when the pressure lowers as the hose empties between pumps. It should be called a "pressure moderator", but it does that by suppressing the surge in each pump cycle.

[Dick_Morris]

A thought on returning the bypass water to the tender at a level high enough to see it returning. This would tend to aerate the water as it squirts back into the tender water. Then the aerated water is returned to the boiler. The aeration could be somewhat reduced by having the "nozzle" where it flows back in the boiler relatively large so that its a gentle flow rather than a squirt.