temperature of your hot well?

[wsmcycle]

thanks for the help to all and Mike>> "Your injector is largely its own economizer/feedwater heater so it is usually piped directly to the boiler." I never considered the injector might impart heat to the incoming water.

This first pump in your closed loop, down line from the condenser, is it a positive displacement pump or a vane pump?
Is the hot well open to atmosphere?
You have a second pump(high pressure) between the hot well and the boiler right? Does it run all of the time? Perhaps it recirculates until you open it to the boiler?

[Lopez Mike]

Yes, the injector imparts a lot of heat to the entrained water. Numbers I do not have in front of me.

A variety of scavenge pumps will work. It just has to be self priming. I have seen diaphragm pumps from a boat drinking water system, gear pumps, all sorts of things work.

The output of the scavenge pump goes to the hot well. No back pressure to speak of. And, yes, the hot well is open to the atmosphere. In fact, many or most are open at the top so that you can see what is going on. A valuable diagnostic point.

Yes, the feed water pump recirculates. Especially at part throttle and light loads like with a following wind. The bypass valve is either manual (got to fool with it off and on) or controlled with a float in the hot well. If you think about it, the total amount of water in the entire system including the boiler and hot well is a constant, If you regulate the volume of water in the hot well, you are automatically regulating the level in the boiler.

The hot well is where most of us add makeup water to compensate for leakage and whistle and blower and burner usage (I use an old tin cup!) And it's an easy place to add the occasional of dollop of chemicals to make the boiler happy.

[87gn@tahoe]

I would encourage you do add an engine driven feed pump to your setup, even if you don't go with a condenser.

In my opinion, on a steamboat at least 3 means of getting water into the boiler is imperative (hand and engine driven pumps, and an injector). I have come to the conclusion that you can rely on injectors to be unreliable, especially so in a marine environment. Pulling out of unsavory water supplies can cause some issues with check valves and such, making redundancy important.

[Lopez Mike]

I concur. It would not occur to me to not have an engine driven pump. Plus they are the most efficient of the various choices.

To explain, the larger an engine is, the more efficient. Simply because the power goes up as the cube of the dimensions and the heat loss goes up as the square. It makes good sense to tap off of the main engine for most of your auxiliary needs such as feed water and/or electricity. The other feed water sources are for backup. If your main engine lacks the reserve capacity for this, then other solutions will need to be looked into.

A consideration when you think about backup pumps is, again, efficiency. One seldom considered comparison is between the two common steam driven pumps, the simple reciprocating pump, either simplex or duplex, and one that includes a flywheel.

The non-flywheel pump has the advantage that it can run at very low delivery volumes. It can just sit there and make an occasional stroke as needed. But the down size is that to operate like this, it makes essentially no use of the expansive properties of the steam. The steam is admitted throughout the stroke. Shades of the 18th century!

A flywheel pump, such as a small single cylinder engine with a pump attached, has to keep running to operate, but the valve gear can be adjusted for earlier cut off like your main engine thus gaining a great deal of efficiency.

I have a Paul Breish duplex pump partly machined but I am aware that it will be a bit of a steam hog. I also have a Stuart #1 and I'm sketching up a piston rod driven water pump for it. I expect that it would be significantly more efficient.

But all of these are backups. The main engine driven pump operates in sync with the speed of your engine and thus needs less attention or regulation.

For sitting around at the dock leaking a bit of steam here and there, and tooting the whistle, a hand pump works great for me.

[wsmcycle]

Mike
"To explain, the larger an engine is, the more efficient." <<<< This only true if you have need for the power.
I have two pumps that came with the Stuart6 castings. I did not finish out and install them because I was anxious to
run the engine and I didn't plan to use them. They looked power hungry even if they were not pumping.
I had a 12v Volkwagen fuel pump on board for a while and it could put makeup water back in at 90#. It died.

[Lopez Mike]

Hmm. I'll have to think that over.

Of course if your engine is so large that it is not working fairly hard at hull speed, that is probably true. But most of us haven't powered our craft that generously.

My Stuart #1 (2 x 2) running at full output (unlikely as a feed water pump) isn't going to be as economical as my 3 x 5 main power. Less than one fifth the displacement (and power) but over thirty times as much heat radiation per unit displacement!

And my duplex steam pump is probably better as a condenser than as a converter of steam energy to water flow! I love to see these things run though. Hopeless techie here.

That 12v pump must have drawn a fair number of amp hours. It seems less than efficient to make electrons and use them to pump water rather than do it directly. I must say I never thought of these new high pressure fuel pumps though.

I hope the experts on here are reading along and will chime in to keep us honest.

[wsmcycle]

I keep the 12 volt pump for backup. I have a small motorcycle battery which can run it for an hour.

[barts]

I use both an economizer and a feed water heater along with the condenser... my thinking is as follows: since the water temperature of what I float in varies from 51 F or so in the San Juan Islands to perhaps 75 or so in some lakes, and I want the condenser to work when I'm at the dock testing, most of the time the water in the hotwell is going to be cooler than optimum. I use the feedwater heater to get the feedwater back up to exhaust temperature - prob. 250F or more; it then goes into the economizer to be heated to boiler temperature.

- Bart

[preaton]

Bart's got it right.
1. Excess cooling capability in condenser means maximum vacuum - good for the engine.
2. Feedwater heater on exhaust so the heat is not going to waste. Probably means smaller condenser required.
3. Economiser in boiler to use waste hot gas.

The question remains "How hot the "hotwell?" In this situation the only reason for a HOTwell is to de-aerate the feedwater. Otherwise a COLD hotwell would be just fine.

If you bypass the feedwater after the exhaust feed water heater back to the hotwell you will certainly warm up the hotwell. But unless the feed pump is drowned too hot a hotwell is a problem as previously mentioned.

If you like complication why not feed the feedwater through a de-aerator like in the big boats? All these were was a sealed chamber with a float valve to control level, connected at the top to the condenser vacuum. The air is driven off by the vacuum.

Probably simpler to use boiler treatment that scavenges the oxygen.

Cheers

Paul

[barts]

One method that might work on a condensing plant w/ vacuum and inboard condenser is to bleed some water back from the hotwell through a spray nozzle back into the condenser. Why do this? Well, the heat transfer between liquid and tubes is much higher than that of steam and tubes, and the effectiveness of jet condensers is well known... so by recirculating water back into the condenser, we increase the efficiency of the condenser significantly. This lets us tune the effective size of the condenser to match the current output of the power plant, and allows us to fit a smaller condenser as well. We could even regulate the amount of recirculation automatically so that the output of the condenser was at 175 F or so, regardless of engine power current in use.

- Bart