Water Pump Question

Hi,

This weekend was the third steam rally for my newly completed DCC. The injector started to play up so I had to rely on the water pump. The pump was not keeping up with filling the boiler. I was only trundling around in 1st gear as I am bedding the engine in.

The pump appears to be functioning correctly. The clack valve ball lift has been triple checked along with the ball lift in the pump and the balls re-seated. The pump feed pipe to the boiler does go cold when the pump bypass valve is in the closed position. There is no water leaking past the pump gland packing. The pump and clack valve have been checked for foreign debris, both are clean.

What should I expect from the water pump? I know it will not deliver the same amount of water into the boiler that the injector will but surely it should at least maintain the water level in the boiler?

Chris

Hi Chris,

As the pipe and clack valve do get cold at least some water seems to be delivered to the boiler.

On Pied Piper I can keep the water level in the boiler about constant when driving, might need to have another look at it as I was told the pump should deliver enough with the bypass at half or thereabouts. Currently I have to put bypass in fully closed   .

Hope this helps

Cheers

Elwood

Hi

If your running in the engine on a rally field I would recommend 2nd gear. Walking speed with the crank going relatively slowely. 1st will have the pistons and rotating parts running much faster. Also your wasting a lot of steam and hence using a lot of water as your not allowing it to do the work and relying on pure pressure than the expansion of steam.

On Crystal I could set 2nd gear and trundle around a rally field just above walking speed and the water pump set to half would slowely fill the boiler. On full in 3rd gear doing 8mph along the road, 1/3 regulator, cut right back on the reverser and had the water pump easily keep up with demand. Rarely needed to use the injector.

My Agri needs quite a lot of revs to put water in via the pump alone. The only time I find it can just manage it is out on the road rattling along at a good pace in top.

Some great responses, thanks all.

Question on the bypass valve setting. I had the bypass valve fully closed, what is the purpose of having it partially open?

Cheers, Chris

Hi Chris,

the bypass allows you to regulate the amount of water to be pumped to the boiler, i.e. to let part of the flow produced by the pump to bypass the route to the boiler. So with bypass fully closed no water is to be returned back into the tender as with bypass fully open all water is returned. Put the bypass to anything between off and on and you can set the amount of water to the boiler to avid to overflow but enough not to let the level drop too low thus empty the boiler.

And yes, Lynn mentioned the right thing, use 2nd gear, made the same mistake myself running in first, but then engine will run much too fast for no reason, using second makes the drive much more enjoyable, unless you drive uphill or with heavy trailer.

Cheers

Elwood

Thanks for that Elwood.

Will see how I get on at the next rally.

Chris

If you have turned the shut off cock plug since assembling and fitting the pump boiler clack there is a possibility the PTFE packing sleeve has turned and is blocking the port into the boiler.

Checked the clack valve and all OK with that.

Reading through these responses the general consensus is the water pump will at best maintain the boiler water level and not at tick over so if your having issues with your injector then you can run into problems Is there a reason why the water pump is geared down? If it was 1 to 1 ratio it would be far more efficient. I'm going to investigate having you gears made.

Chris

If you speed up the pump you will run into problems with water hammer on the delivery side, and probably cavitation as the water won't be drawn up the suction pipe fast enough. You do not need to constantly feed water into the boiler of a traction engine. Keep the pressure up near the red line without wasting steam by having the safety valves lifting, if you run at a lower pressure you will use more water. If you are managing the boiler properly and watching the water level and ground conditions - ie you're either going uphill or down then you shouldn't find yourself with no water in the glass.
Use 2nd gear for pottering around the rally field and 3rd for road use, and link up on the reversing lever.

If for example you're on the road and have a hill coming up fill up the glass to about 3/4, the increased draught from the exhaust will increase the steaming rate and with water and pressure in hand you should easily tackle the hill, if you know you have a downhill section coming up if the engine is making steam top up the water level before you reach the top and shut the damper to quieten down the fire, on the road locomotive so long as you can see water in the gauge glass the firebox crown is under water. Personally I don't use the pump at all, it is there purely as a standby means of feeding the boiler. Using the injector adds warm water which is less of a thermal shock to the boiler.

The pump can loose water internally due to the suction valve not seating and around the by-pass valve - just because the handle is in the shut position doesn't mean all the water is going into the boiler, likewise if the PTFE seal in the boiler check valve has turned this will block the port into the boiler.

Hi all,

Been away for a week and thinking about this pump. One thing that has always seemed wrong is the amount of washers I had to add to get the correct 1mm ball lift. Looking at it this is definitely restricting the water flow through the outlet hole, I can only assume that the seat has been machined too low.

I'll give STW a call on Tuesday.

HI Chris

The flange is 2.5mm from the matting surface so looks about right.
It could be the depth of the bore. It may have been machined a bit deeper to "clean up" the seat area.

The depth of the seat is 20mm from the flange.

On the photo you've posted there seems to be a blowhole in the casting part way down the bore to the seat, it may be allowing water to return to the suction side.

I'm 22mm to the seat so all good.

Chris