Help with water pump - no pressure

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Glenn Brooks
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Location: Woodinville, Washington

Help with water pump - no pressure

Post by Glenn Brooks »

Hello all,

So today, ran the loco and could get very little pressure out of the water pump, less than 50 psi on the high pressure side with the shutoff valve closed into the boiler. Sort of stumped and looking for suggestions where to start troubleshooting.

So far, the possibilities are:

1) pump can’t build pressure, or
2) return line and needle valve allowing to much pressure to bypass the input line- bleeding off any high pressure, or
3) 1/8” boiler injection line to small a diameter??

The pump is a simple single acting cylinder with 5” stroke, 1/2” diameter. The shaft is 1/2” round stock with a slip fit into the bore. Less than .001” clearance in the bore - no “wiggle room” when the shaft is inserted into the bore. Also, no water squirting out of the pump from excess clearance. The pump does Push small quantities out of the high pressure side, when I break the connection at the boiler - but with no significant pressure.

The pump shaft is plain round stock- no O rings to seal the bore.

Here is a pic of the new plumbing- showing 3/8” low pressure input line from tender, into pump. 1/4” return line to tender, and 1/8” high pressure line leading to boiler input. Check valves on both sides confirmed working properly. The pump body and attached output Tee fittings are painted blue, located right at the level of cross slide, is photo. The high pressure line exits from the left side of the tee, thence runs up to the check valve on the footplate, and forward into the front of the boiler. The return line exists the rear of the tee, runs back to the cab, they a needle valve, and down into the tender feed water line.
1651841B-88F5-469D-A792-EC4EFA4E19AC.jpeg
Any ideas where might be the most likely place to start looking/fixing?

Thanks
Glenn
Moderator - Grand Scale Forum

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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NP317
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Re: Help with water pump - no pressure

Post by NP317 »

Glenn:
If the return needle valve is open even a slight amount the pump pressure will drop significantly.
So pressure should be measured with that return valve completely closed.
RussN
RET
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Location: Toronto, Canada

Re: Help with water pump - no pressure

Post by RET »

Hi Glenn,

If I read your description correctly, there is no "O" ring to form a seal on the pump ram. You are going to need one, either on the pump ram itself, or in the pump body to make a seal around the ram. Just don't put one in both places.

If there is no seal on the ram, then on the suction stroke, air will be pulled in past the ram, so there will be little or no pressure built up on the discharge stroke. This is one way to get the performance you describe. This also assumes that all the check valves are working. I like "O" rings, so I usually like to use one as a "soft" seat for the stainless ball to seal on. I've found that I have little to no trouble with that system. As a side benefit, the ball doesn't bounce around since the hysteresis of the rubber dampens out any bounce immediately.

Also, for the size of your engine, 1/8" dia. tubing is way too small. It should be no smaller than the return line back to the tender. If you think about it, at one extreme, all the flow will be going to the boiler when the return valve is closed and at the other extreme, all the flow will be returning to the tender when the valve is fully open so both lines need to be the same size (at least 1/4"). If the tubing is too small, the engine will be "Jerky" at high speeds, because the back pressure on the pump ram will limit how fast the axles can turn.

Hope this helps.

Richard Trounce.
Glenn Brooks
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Location: Woodinville, Washington

Re: Help with water pump - no pressure

Post by Glenn Brooks »

Thanks Guys, Much appreciate the quick input.

Russ, I think I will replace the needle valve. It appears to be original equipment. Even with it closed tightly I seem to get a squirt of water through . So likely the seat is suspect.

Richard, thanks for the comments in size of the line. Makes sense that HP feed and return might carry same amounts of water. That would make them both 1/4”.

Also, to confirm your comments - indeed there is no O ring in the pump. So I’ll machine a little grove in the ram and install one.

Btw, I went back out and isolated the HP input side - tightened up the packing gland on the pump and got cycles of 150 to 250 PSI. Also the ram is undersized on the back end of the pump, wobbly in the bore by at least .005” - .010” . Also found a leaky flare fitting on the return line, between the needle valve and the pump- likely a pressure leak also.

So will renew these faults tomorrow and try again.

As they say:
What’s the definition of a steam engine: “one damn thing after another....”

Thanks much,
Glenn
Moderator - Grand Scale Forum

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....
Pontiacguy1
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Location: Tennessee, USA

Re: Help with water pump - no pressure

Post by Pontiacguy1 »

If you have a packing gland on the ram of your crosshead pump, then you don't need to add an O ring. Crosshead pumps work off of displacement, but they DO need to be sealed. IF they get any amount of air leakage, they won't be able to prime. Being able to seal off the ram will be good enough.

Ditto what was said about your line size: It must be large enough to easily take the entire flow of the pump, either to the boiler or to the tender. If it is constricted, then you are going to build up a huge amount of force/pressure on your pump ram, body, mounts, etc... That will also cause a lot of back pressure, surging, and could even lock it up or cause damage to things.

One time some trash got into my exit check valve on the axle pump of my 2-10-0, which weighs about 800 lbs or so. I was running along about 5 mph, and all of a suddenly the whole engine came to a sliding stop! Just from the axle pump! Cleared out the check valve, and everything was fine. Didn't do any damage, but it easily could have ripped the pump off of it's mount or something.
Rwilliams
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Re: Help with water pump - no pressure

Post by Rwilliams »

What scale is the locomotive?

All boiler feed water supply lines should be as free flowing as possible with as few right angle bends as possible. The 1/8 diameter tubing is definitely part of the problem. Straighten out the supply line from pump to the check valve as much as possible and use at least 1/4 inch tubing.

Long ago when injectors were still more like black magic, steam boilers were supplied with crosshead pumps and the pressures developed at higher speeds were more than the pipes and fittings could handle sometimes. There were reports of split pipes and ruptured castings all the time.

Long ago there was a guy who built a 1.5 scale shay with an axle pump for boiler feed. It could not make it around the track without running out of water even when the pump supply line was wide open to the boiler. A beautiful locomotive but it just would not feed water. The owner builder eventually passed and the locomotive was sold to a new owner. First thing was to remove most of the 90 degree elbows restricting the water flow from the pump to the boiler and the big shay could now make it around the track without running out of water.
Glenn Brooks
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Location: Woodinville, Washington

Re: Help with water pump - no pressure

Post by Glenn Brooks »

Thanks all,
Back to work on the pump problem tomorrow.

Rwlliams. The loco is around 2.5” scale- kind of a freelance 4-4-0 design by Herb Ottaway in 1950. 12” boiler, 12” gauge. I’ve just been staying with the existing plumbing, but plan on converting the hi pressure side to 1/4”,per suggestions above.

Also plan on replacing the packing gland material with new packing. Picked up some nice graphite string from a fellow live steamer the other day. I tightened up the gland and did get some 150-200 psi spikes, pushing the old girl back and forth on the track. So concentrating on the packing gland, and fixing a couple of leaks caused from bad flares.

It’s good to get solid background on pipe diameter and flow... Will report results back after the work...

Glenn
Moderator - Grand Scale Forum

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....
RET
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Re: Help with water pump - no pressure

Post by RET »

Hi Glenn,

Given the size of your locomotive, I think that 1/4" tubing is on the small side. 5/16" or 3/8" would be a better choice. You should go at least one size bigger on the suction side because you only have 14.7 psi to push the water to the pump (sea level atmospheric pressure. This is even more important for an injector.

At low speed, the flow will be OK, but you need to size so there is very little pressure drop in the lines at the highest speed you can run at. Having too small lines just wastes power and can even break something as other posters have mentioned.

Hope this helps.

Richard Trounce.
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Fender
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Re: Help with water pump - no pressure

Post by Fender »

Sorry you are having trouble with your pump. But assuming you get it working properly, would it be oversize for the engine? By my calculations, a 1/2” ram with a 5” stroke will pump about one gallon of water for each 250 revolutions. What size are the cylinders?
Dan Watson
Chattanooga, TN
Kimball McGinley
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Re: Help with water pump - no pressure

Post by Kimball McGinley »

Many crosshead pumps like this featured some sort of accumulator to balance the flow. This was the large round or cylindrical object on the pump. It provided an air cushion that stored some pressure during the discharge cycle. That might help too?
Pontiacguy1
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Location: Tennessee, USA

Re: Help with water pump - no pressure

Post by Pontiacguy1 »

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.

Most of these crosshead pumps were oversized anyway, so that you can throttle them back with a fine bypass valve or just turn them on and off when needed, via your bypass valve. Same for injectors... you want to have extra capacity in case your water gets low and you have to make it up quickly.
Glenn Brooks
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Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: Help with water pump - no pressure

Post by Glenn Brooks »

Hi all,

Hard to believe it’s been three years since my last attempt to fix this cross head water pump. haha. COVID lockdown and cardiac arrest soaked up a big chunk of time…

Anyway my summer goal is to finally make my water pump pump. Per thread recommendations above I plan on moving ahead with larger diameter pipe, eliminating the 90* bends, and sourcing a larger size commercial needle valve for the larger diameter pipe.

Which brings me to my one big question: where is the ideal location to install the needle valve?

As a given, I want to physically locate it at the backhead - where I can easily adjust water flow when the loco is in motion. So,,,

Should I run a high pressure loop to the backhead/footplate area so I can regulate water flow directly into the boiler on the high pressure side of the pump, or, is it OK to just put the valve on the return line back near the tender?

Clearly, The return line to the tender is the cleanest install. But questioning if this is the best and most efficient location in the system to install the valve.

Logic suggests metering the return line water flow/pressure at the backhead will indirectly adjust the flow of water into the boiler…. But is this actually true in practice?

Also, I want to use best live steam practice on this, but don’t know what that best practice is… any suggestions greatly appreciated!

Thanks,
Glenn
Moderator - Grand Scale Forum

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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