injector plumbing

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barts
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injector plumbing

Post by barts » Sun Jul 15, 2018 2:09 pm

Hi folks -

I'm replumbing Rainbow's steam line & boiler feed as they are literally underfoot and make two spots in the cabin suitable only for really small people. The previous owner used two separate boiler checks, one for the injector and one for the engine driven Hypro pump (there's no hand pump, which is a fault I will remedy). I'd like to use (starting at boiler) 1. boiler shut-off valve, 2. lift check (sans spring but mounted so gravity helps) 3. pipe tees to plumb in injector, engine pump and future hand pump, plus pressure relief valve in case boiler shut-off valve is closed. The Hypro and injector would have their own check as well; the hand pump will use commercial checks anyway. And yes, there will be a union after the lift check so I can setup the plumbing on my bench instead of on my head in the boat.

I've never installed an injector (3/8" Penburthy) before, and I'm wondering if two checks will provide two much back pressure, or are these things pretty tolerant of such? I'm going to use a lift check for the injector as well to reduce the back pressure.

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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gondolier88
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Re: injector plumbing

Post by gondolier88 » Mon Jul 16, 2018 8:10 pm

Bart,

When you say 'starting at the boiler' I assume from the description that you mean your'e working upstream from the boiler inlet?

Injector pipework should provide as linear a flow as possible and as little resistance as possible- do not introduce elbows or tees in the injector flow unless absolutely necessary (use the through bore of the Tee, not the branch). Try to keep checks to minimal amount- no injector is created equal or identical to another in my experience, and while I have piped up an injector through two checks with no issue, I have also piped up an identical one that would absolutely not put up with the extra resistance.

On the checks- why remove the springs?

Don't bother with a relief valve on the supply- it will develop leaks, it will be pita, it will never be used in anger as no one should be operating a steam plant without first opening the water supply before lighting the fire.

If its a standard Penberthy they generally like to have a little amount of lift rather than flooded. Always size the delivery pipe to be the same bore as the steam supply to the injector and make the water supply equal bore or larger.

Greg
Don't get heated...get steamed up

http://www.simpsonboatbuilding.co.uk
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barts
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Re: injector plumbing

Post by barts » Tue Jul 17, 2018 2:14 am

Yes, upstream is what I meant. The previous owner had used inline check valves, but my experience with them is poor - if something gets in, once gets to disassemble the plumbing to fix it, whereas with the lift checks, all I need to do is shut off the boiler stop valve, and pull the top of the valve. I've removed the springs from lift checks to reduce the extra 'cracking pressure' they add, but you're then required to install them horizontally so gravity tends to keep them closed.

Good advice on the lift rather than flood for the supply, and sizing the other lines, thank you.

If you've had trouble w/ two checks, I'll stick to a single check for the injector and have the rest of the pumps share another.

I always fit a relief valve for the engine driven pump. I've seen valves moved by accidental foot motion before, and blowing the boiler freed plumbing a few miles from shore in open water is not my idea of fun :).

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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