Help with water pump - no pressure

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Charles T. McCullough
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Re: Help with water pump - no pressure

Post by Charles T. McCullough »

Further reflection on the surge suppressor: If the pump can move more water than the size of the pipes and valves can accommodate can be a reason to include the surge suppressor NEAR the pump. So that on the pressure stroke, the pipes are not subjected to over pressure for any joints, bends or valves in it. Even if the end of the pipe is open to atmosphere, there can be excessive pressure at the output of the pump if the water cannot travel to the end of the pipe as fast as the ram is attempting to displace it from the pump cylinder. I suppose the entire length of the piping from the pump to the end should be capable of passing the volume of water the pump can output, this includes all one-way valves, elbows and curves in the pipes.

Conceivably, an axle pump could lock the drive wheels if enough pressure exists in the output pipes of the pump. The drive wheels cannot rotate any faster than the pump can move water or "somethings gotta give"!
Glenn Brooks
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Re: Help with water pump - no pressure

Post by Glenn Brooks »

Yes, I actually blew out a new bronze elbow in my water injector line once, due to a blockage. Pressure build up ruptured the fitting. Iam looking for a small 250* pressure relief valve to guard against pressure spikes, as an alternative to a surge tank.
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Bill Shields
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Re: Help with water pump - no pressure

Post by Bill Shields »

Please define "water injector"
Too many things going on to bother listing them.
Glenn Brooks
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Re: Help with water pump - no pressure

Post by Glenn Brooks »

Bill, sorry, not a very descriptive term. The fitting was a new black iron coupling on the high pressure side of the water pump - feeding water into the boiler.

Glenn
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Bill Shields
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Re: Help with water pump - no pressure

Post by Bill Shields »

Ah..ok...what type of pump that developed that pressure?
Too many things going on to bother listing them.
Pontiacguy1
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Re: Help with water pump - no pressure

Post by Pontiacguy1 »

You absolutely CAN have surge pressure in your piping when you are running an axle pump or crosshead pump at high speeds, or if you turn it on suddenly, aka block the bypass suddenly. The more line length you have and the more elbows, check valves, etc... the greater the hammering effect of the water will be. A sticking check or something partially obstructed will greatly contribute to this. In the smaller scales the volume of water isn't that much and it isn't a huge deal, but the larger the pump volume, the larger the hammering effect. That is why prototype locomotives which used crosshead pumps all had surge chambers built right over the top of the pump. It is nothing more than an air chamber with the output of the pump about half-way up inside the air chamber, and the outlet from that chamber to the boiler check down low. Thus, the whole thing will not fill with water and the upper half (above the inlet from the pump) will stay filled with air that will compress/expand as needed to help smooth out the pulses and pressure spikes, at least somewhat.

I don't think that a surge chamber would be necessary on any 1 1/2" scale locomotive or really even a 12" gauge locomotive, but it also won't hurt to have it there. Just making all your piping the next size larger will mitigate most of the surging and pressure spikes on a small locomotive.
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Charles T. McCullough
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Re: Help with water pump - no pressure

Post by Charles T. McCullough »

The first time I did a boiler pressure test, I didn't remove the safeties, I completely filled the boiler and used the tender hand-pump to pressurize the system. I figured I'd have to pump the handle a lot and then really pull on that handle as the pressure built! I filled the boiler as full as I could, put the plug back in the fill hole and pulled the handle ONCE and water shot out of both safeties all the way to the ceiling!

Like spilled milk it went everywhere!

After drying off many things in the room, I held down the safeties with the fingers of one hand and pulled the pump handle one more time with the other. No effort at all and the cheap tiny pressure gauge that came with the engine was pegged!

I let go of the safeties and had to dry off everything again.

I removed the tiny pressure gauge and plugged that hole in the boiler. I removed the safeties and plugged those two holes. I got out my "real" pressure gauge (a 10-inch diameter brass antique from a steam traction engine.. or so I was told at the ye olde antique shoppe). The dial goes to 375 PSI. I connected it via a rubber hose to the fill hole of the boiler. (I filled the hose with water to eliminate as much "compressible" air from the system as I could). Two EASY pumps on the tender pump and the rubber hose developed an aneurism and burst.

Another trip round the room with a towel.

I replaced the rubber hose with a brass (K&S) tube and one compression elbow (threaded into the fill port) to a compression fitting and some threaded adapters to the antique gauge.

Two more EASY pumps and the antique gauge was pegged.

It was then that I realized that poor little boiler was probably not designed for that kind of pressure, so I loosened one of the safety plugs (with a towel over it).

I dried the outside of the boiler, retightened that plug and pulled the pump handle one more time about half way and the antique gauge registered 150 PSI. I left it like that for about 20 minutes while I inspected the boiler for leaks. The pressure did drop over time and I noted some water around one of the safety plugs and the plug where the tiny pressure gauge attached. I figure most of the loss of pressure was back through the clack valve and the valves in tender hand pump. But no water at any of the seams of the boiler.

I did that once a year when I was going to run one of the engines (haven't run for several years now). I also tested the safeties by putting one in and monitored the pressure gauge for when the safety lifted as I pulled the pump handle. They both start weeping at about 75 to 80 PSI. They do trip faster when the boiler is in steam. Quite satisfying to have one let go while steaming up or while running... POW!-HISSSSSSSS-pop!
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Bill Shields
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Re: Help with water pump - no pressure

Post by Bill Shields »

pontiac:

I apologize for not being clear.

when I said 'surge not a problem' I was specifically referring to model locos...
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Pontiacguy1
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Re: Help with water pump - no pressure

Post by Pontiacguy1 »

Ok. I might have been confused. Won't be the first time.

I have seen it be a problem on a model locomotive before, but the reason was usually a mis-sized check valve or return line that was too small and not allowing enough flow. Thus the poor pump would sound like a muffled air chisel when you cut off the return pipe. Or with the return all the way open there would be a lope or surge felt when rolling along not under power.
Glenn Brooks
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Re: Help with water pump - no pressure

Post by Glenn Brooks »

Interesting conversation here. My water pump - the one that burst the fitting - is a simple, one cylinder 1/2” x5” shaft working back and forth with a mechanical linkage to the steam chest rod. It’s been some years ago now, but I remember test running the loco about 200’ down the track when the fitting burst. Apparently I either accidentally closed the valves, or incorrectly installed one of the check valves, blocking the intake into the boiler. Can’t remember now, what the exact cause of the blockage was.. but pressure built up by the pump, in the closed system 1/8” pipe at the time, definitely exceeded the 250 psi rating of black iron pipe and split the (new) fitting just as if it had been filled with water and frozen in the dead of winter in Alaska. Very impressive.

Anyway, I’ve since learned that all 1/8” and 1/4” copper and black iron water fittings are generally rated to 250psi. I also just received today a nice little ASME 250psi in-line safety valve for installing in my water pump, high pressure side plumbing. No more blown fittings! And no risk of the water pump system breaking something more important - like a side rod or piston.

Tomorrow the new routing gets bolted back on. So hope to post a couple of pics of the new, straight thru plumbing - basically now, only one 90* curve into the boiler from the gravity feed side of the tender… hooray, hopefully. Looking forward to a successful test run over the weekend.
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Bill Shields
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Re: Help with water pump - no pressure

Post by Bill Shields »

Having a surge chamber yould not protect in that case...only put off the inevitable by a couple of strokes.

Positive displacement pumps should never be installed in such a manner to allow being dead headed.

If nothing else, a safety on the discharge.
Too many things going on to bother listing them.
Glenn Brooks
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Re: Help with water pump - no pressure

Post by Glenn Brooks »

Bill Shields wrote: Mon May 22, 2023 5:17 am Ah..ok...what type of pump that developed that pressure?
The pump is just a simple 1/2” diameter shaft moving back and forth in 6” length of bronze stock…

I have installed a 250 psi safety valve. Wasn’t one on the system previously.

Here’s a couple of pics of the plumbing. The intake line is the lower one. Discharge is the one on top, rising out of the T and bending 90* to the rear of the engine. Still need to reroute the discharge line back into the tender.
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
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