Feedwater Pump Water Temperature

[JonRiley56]

Hi All,

Ron Rogers (aka Detroit Tug) is building a water pump for me from a set of castings that I had sent over from the UK. It is steam driven so I will get to play with 2 steam engines on my boat....... . Does anyone have a feel for what temperature water a pump like this would be able to handle ? I am still musing over my preheating options. Ideally I would preheat after the pump, but the neatest way to "hide" the preheater involves putting it ahead of the pump.

I have sent an Email to Bob Potter who is now handling the line, but thought some of you might have an opinion.

jon

http://www.southworthengines.smartemail ... _pumps.htm

[JonRiley56]

BTW, It is the 12 inch pump.............

[marinesteam]

Jon,

I was thinking about getting the 12" Southworth pump sent from the UK. Did you have any troubles with shipping or customs and what are your impressions of the castings (quality)?

Pics?

Ken

[fredrosse]

The maximum allowable pumping temperature depends on three variables:
1. Pump packings and seal materials suitable for the temperature, probably not an issue here.
2. Pump Inlet Check Valve differential pressure to open. Some pumps with a spring loaded ball type inlet valve will require considerable differential pressure to open. If the water is hot, the maximum differential pressure to open the suction valve will be reduced by the vapor pressure of the water, approaching 1 atmosphere at 212F.
3. Pump speed and suction line velocity. For a reciprocating pump of this sort, keep the suction line as short as possible, with a maximum suction stroke velocity of 2 - 3 feet per second.

[JonRiley56]

Hi Ken,

I didnt have any issue with customs etc. The shipping is very pricey though, around $200 or so. Ron can comment on the quality of the castings etc if he sees this post. He might be able to put pics up too.

If you sweet talk him he might build one for you, but I know he is busy.

jon
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Fred,

Thanks as always for the info. I will probably get back with you when I get the unit and am putting it in. I should probably just plan on preheating after the pump and figure that out. It would make live simpler. Are you done with the Margaret S for the year ?

jon

[DetroiTug]

Hi Jon,

The O-rings for the steam piston and water piston appear to be of the same material. So what's good for the goose is good for grandma- er something like that..

-Ron

[JonRiley56]

Thanks Ron,

I have never goosed a Grandma, but to each his own........ . I did get the following from Bob Potter, the Southworth guy, and it suggests the same.

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Hi John

I have been considering your question and can see no problems with heating the water. On my loco the saddle tank sits directly on top of the boiler with just steel bands between and no insulation. I did this to heat the feed water. I have never measured the tank temperature but it does get hot!

I then had a chat to a couple of guys at the club and they also do not have a problem.

Sorry for not providing engineering facts but practical experience seems to suggest do it. Hope this helps.

Bob

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[Lopez Mike]

To rephrase the advice, the hotter the feed water, the more problem you will likely have with the water flashing into steam under negative pressure (suction) on the input of the pump.

If the hot well is up at the level of the pump input and there are no obstructions, like kinked pipes or heavy check valve springs, then you can get away with a lot. Most feed water pumps don't handle vapors and gasses very well if at all.

This really comes to bite you with injectors, particularly small one. I've spent too much time putting cold water soaked rags on small injectors to be unaware of the problem.

Nothing obscure here. Just that the boiling point of water rises with pressure and drops under a vacuum. They used to measure the heights of mountains by taking the temperature of boiling water. It's a bitch to cook a potato on a mountain. Takes forever! That's why we use a pressure cooker when possible.

Mike