boiler pump return

is there any advantage to having unwanted boiler axle pump water returned to the tender as opposed to just keeping it in a return loop?

The conventional return to the tender is in effect an open return loop interrupted by the bypass valve. Wouldn't you would still need to locate a bypass valve somewhere in the circuit ? In a closed return loop would the axle pump not be acting against itself ? I work in Gauge 1 and these circuits can be very fiddly things to do at this scale so I am all for any simplification but I am not sure about this one.

Mick

Hi Fizzy,

All of the pumps that I have seen/used have the bypass returned to tank. If it is in a closed loop there is a possibility of trying to pump water into a closed system that does not have enough volume and over stress the pump or try and suck a vacuum if the pump cannot get enough water. Both are bad for the pump.

Paul.

I'm not sure I've quite understood your question Fizzy.

The axle pump is either putting water into the boiler - when required - or not (if the boiler is "full" )

The surplus water (via the bypass) either has to be returned to the tender or just be discharged - there is no where to store it as such. So returning it to the tender saves water.

I may have missed the point of your question but the simple answer to your question appears to be - yes, there is a good reason to return surplus water to the tender...

Regards,

IanT

Edited By IanT on 12/06/2015 09:17:59

I think what Fizzy wants to do is return the bypass water back into the pumps feed pipe to save having to run it all the way back to the tender. As this would still be an open loop I can't see a problem, end of feed pipe is still open to the tender.

Red would be the usual return pipe

Edited By JasonB on 12/06/2015 09:26:55

If there is a check valve at the tank could be a problem if not should be OK

This is how you'd do it when regulating a centrifugal pump in industry. The only advantages of sending it back to the tank are

1 you can see that the pump is moving some water, it doesn't guarantee that any is going into the boiler (been there, done that!)

2 better clearance of any air in the system

3 less heating of the water, but you'd have to be recirculating a very high fraction of the flow for this to be a problem

You would still need a bypass valve to regulate/balance the amount of water going into the boiler. The bypass valve is traditionally mounted on the tender.....maybe because there is room for it there....but it may be difficult to find a convenient location for it elsewhere.

Mick

I think Duncan has hit the proverbial nail on the head - the great thing about returning the water to the tender (or side/saddle tank) is that you should position the return so you can see the end of the pipe.

So when the bypass is closed, the pump is (hopefully) putting water into the boiler, and no water comes out of the return. Opening the bypass valve allows water to squirt from the end of the return pipe into the water reservoir. And adjusting the bypass (evidenced by the amount of water squirting from the pipe) enables you to control the amount of water actually going into the boiler.

thanks all - I had assumed you would all 'get' the scenario which is as Jason suggests, sorry for that. I take onboard the seeing water return part but I done ever recall seeing a tender where this was the case, least not at our track. Im planning on installing a pressure gauge for the water to determine its ability to pump.

We have a bleed valve on the outlet of our pump which is at a convenient hand height. Makes it easy to check pump operation (and prime if necessary). The outlet points sideways which is good for spraying spectators with water.