feed water by-pass

[johnp]

How do i hook up a feed water bypass? just throttle down the intake side of the pump? or do i make a loop from the output side to the intake side with a valve in-line.

John

[87gn@tahoe]

Valve after pump discharge, back into hotwell.

[johnp]

no hot well. can i go back into the pump?

[farmerden]

Where is this surplus water coming from? Storage tank? put it there! Why no hotwell?

[fredrosse]

My feed pump bypass is connected right back into the pump suction pipe, works fine. Could be back to hotwell, back to feedwater tank, back to lake or river, all OK.

Throttling shut the feed pump suction valve would also reduce feed flow to the boiler, but that would most probably cause problems with the pump, should not be done.

On the discharge side of the pump, since there is a valve between the pump discharge and the boiler, you may have to have a relief valve to protect the piping between the pump discharge and the boiler valve. This depends on the pressure capability of the pump, and most small reciprocating pumps can produce outrageous pressures if the discharge is blocked shut from the boiler. There must be no valve between the pump discharge and the relief valve.

On my steam setup, the engine driven pump could produce well over 5000 PSI if there was no relief valve, so I have one on that piping. My manual pump cannot produce so much pressure, if I stand on the pump handle, only about 250 PSI is produced, and the piping is good for well over 500 PSI, so this pump discharge does not need a relief valve.

[barts]

I don't think returning the pump bypass output back to the pump suction is a good idea; it makes it very hard to get air out of the line. Dump it someplace where air doesn't hurt. Also, plump your pumps in series so that you can use the handpump to purge the engine driven pump of air. This doesn't matter much if you don't trailer the boat or drain it frequently, but not fighting airlocks in the feed pumps is definitely a win.

Don't forget to fit a strainer on the input to the pumps. Nothing hangs a check valve faster than pine needles in my experience.

- Bart

[johnp]

Thanks guys, i have not hotwell. Coming directly from the lake. One main supply to all three pumps. I'll add the relief .

[Lopez Mike]

Perhaps you should consider having a hotwell. The reason being that it is very convenient to have a simple system of automatic boiler water level control. That simple way is to have a hot well with a float valve. The float valves I have seen over the years do not lend themselves to any installation other than in a hot well.

In case this isn't clear, the float valve is the bypass after the engine driven feedwater pump.

This system has proven it'self many times over the years. You will have many things to deal with while steaming and not having to constantly fiddle with the bypass will be most welcome.

Also, while you may be steaming in fresh water most of the time, not all 'fresh' water is something you might want in your boiler. I've seen some pretty gunky looking stuff alongside.

Mike

[johnp]

I don't understand how tha float switch would work as a bypass. Once I set the bypass valve shouldn't it be left until I change speed? What type of float valve would I buy? Would it just maintain the hotwell level from the lake via lake water pressure or would I need a pump?

[Lopez Mike]

Looking back at my post, I realize that I left something out. Not a first for me (ahem).

A little background:
My steam experience has been strongly biased towards non-condensing installations. In my case, railroad locomotives. The one I did the most work on was a 90 ton Shay geared locomotive. The water supply was from city drinking water, hardly polluted. Every year I would have the boiler open for inspection and repair work. And every year I would marvel at the quantity of deposits in there.

I understand the attraction of getting your feed water from the lake or river. But my experience has been that you are far better off to go to the trouble of adding a hot well and (my omission!) a condenser and go to a closed system. Your boiler will thank you.

You will have control over the chemistry of your boiler water. You will have the option of adding some vacuum on the output of your engine. You can use feed water heating that starts from the hot well temperature rather from the lake temperature. And there are other good reasons. Other, more experienced members will comment, I hope.

Probably the only drawback that comes to mind, beyond the extra effort at construction time, is oil removal. On single expansion engines at moderate pressures and temperatures, there is considerable experience with not internally lubricating the engine.

What I was trying to say before was that with a condenser and hot well, you will have a closed system with a constant total volume of water. Thus when you regulate the hot well level, you are also regulating the boiler level.

The feed water pumps all suck from the hot well. The float bypasses from the output of the engine driven pump back to the hot well.

Also, the hot well is a great point to see what is going on with the total system. You can see water returning to it from the float valve and from the condenser.

Think this all over before discarding the idea of a closed system. You will, in addition, have a lake full of makeup water. Something that we salt water denizens do not have.

Mike