water pickup

[Lopez Mike]

My air hose on my feedwater output line has several things going for it besides that fact that I picked up a pile of it surplus for very little cost.

It isn't plastic stuff imported from who knows where. It's 150+ pressure rated woven and rubber covered (imported from who knows where, actually) and is in regular use in such carefully controlled environments as Mexican tire shops. Tough stuff.

It is on the opposite side of the check valve and safety shutoff valve from the boiler.

It's easy to route in weird places.

I use ordinary barbed end fittings with a hose clamp. On the one time when I started running the engine without opening the boiler feedwater valve when under observation (she was cute), the pressure slowly forced the hose off of the barbed fitting and I got a face full of cold water (I thought her laughter was immoderate). Since then I have fitted a relief valve. Harrumph!

Been running the stuff for two years now. The wobbling of the feedwater pressure gauge dropped from +- 30 lbs. to less than 5. What with the glycerine filled gauge, it almost looks like I know what I'm doing.

It a choice, indeed.

[fredrosse]

One issue that deserves consideration: Valve Leakage In power plant design, we always must assume that any valve might leak, as a matter of fact we have "Leakage Class" definitions for any valve. The potential issue is back leakage of hot, pressurized boiler water back into the feedwater piping when the check valve leaks. Yes, the feedwater piping is obviously higher pressure than the boiler it feeds, but I would not recommend using Home Depot PVC pipe for feedwater lines, although it is rated for several hundred PSI. That is because it is only rated for that pressure at ordinary "room temperature".

Be sure you can remain in good conditions if any valve might leak, all of them do leak sometimes. Steam hose rated for 250 PSI / 406F id available, but fairly expensive.

If you are not using piping that is rated for boiler temperature, how do you handle back leakage potential? In some cases you can just assume you will row home if the hose bursts, but do consider potential burns, etc. Similar to the unexpected breakage of a sight glass, it can happen, so we protect against flying glass, and have an alternate means of finding boiler water level, try cocks.

As an aside, the power plant design rules also state that you cannot count on a valve leaking, you have to design for a valve leaking, or not leaking.

[cyberbadger]

One issue that deserves consideration: Valve Leakage

Thanks for another excellent post, and it actually hits on a point that I am mulling over for my own new ASME boiler. And also something lighthouse will have to deal with his boiler.

Namely - if you have a water input nozzle/inlet what are safe ways to plumb 2 feed water sources into that one boiler inlet.

In my case my new ASME boiler has 2 inlet/nozzles, but I plan to use 3 or 4 sources. (2 injectors, 1 steam pump, and most likely also handpump - probably the Neptune)

Lighthouse's boiler has 1 inlet. He's got a quality handpump. And I hope he's getting a second - whatever he chooses.

It's a lot cheaper for Lighthouse because his MAWP is 95PSI.

My MAWP for my new ASME boiler is 200 PSI. Class 250-300 valves are a lot more expensive.
I've already have new ones for almost everything I could think off - but not this combing of 2 feedwater sources into 1 inlet. An over sight on my part - I would have asked for 2 more inlets and could have gotten them free - but that ship has sailed. My ASME boiler has been stamped and I have a copy of the P2 that has been filed with the National Board.

In my case any valve (check, ball, globe) is $40-$200. :/

So what are good safe ways to plumb/pipe/fit two feed water sources into 1 boiler inlet?

-CB

[gondolier88]

CB,

The only acceptable way to do this is to use feedwater manifolds- just as with steam take-off; isolate the manifold with a valve on the boiler- this means that although the manifold will effectively be a part of the pressure vessel it can be isolated. Make up the manifold in heavy steel fitting, preferably silver soldered or welded. Each sprue will need it's own check valve, then pipe upto each one in the normal manner.

Greg

[DetroiTug]

"It's a lot cheaper for Lighthouse because his MAWP is 95PSI."

All small amateur hobby steam plants should use Class 300 (schedule 80 ASTM A106 seamless) piping and valves. Schedule 40 is permissible per the code IF the person or organization using it can perform proper load and stress analysis. Water at 212°F and 0psi can still injure someone very badly. Our steam hobbies put the operator and occupants in very close proximity to the boiler and piping, it's simply not worth the risk to use anything less than the correct piping. This sounds harsh, I've heard people say it's too expensive, they should find another hobby.

"So what are good safe ways to plumb/pipe/fit two feed water sources into 1 boiler inlet? "

I have 5 going in to the same inlet with two isolation and check valves. Yes, I've had trouble with check valves, but that wasn't the reason. The feedwater inlet and associated piping up to the first check valve is the most dangerous bit of piping in any plant. If that breaks it's going to be disastrous. The lesser there are of it the better. A good way is to come out of the inlet with schedule 80 class 300 to the isolation and check valve immediately and then run copper to the feedwater sources. This reduces the torsional loads on the fitting in the boiler. A long run of pipes with a lot of fittings and insufficient support can put an excessive stress on the associated threaded joints.

Back to schedule 40. Take a piece of it someday and slit it in half in the threaded section and notice thickness in the root of the threads. And too, nowadays almost all (Home Depot and Lowe's)1/2" schedule 40 pipe and fittings are imported from the folks that have been helping us out with our manufacturing for the last 30 years. The quality is very poor. I've machined it, the steel looks like it's loaded with cinders and shale. It just smears worse than 1014 which is considered the lowest grade steel. Other sizes like 1/8" and 1/4" are still manufactured here. The price and quality reflects that. The guy at the plumbing place said all 1/2" sch 40 A53 comes from China. There is none manufactured here in the states that he knew of.

-Ron

[fredrosse]

I agree with most of what Ron says above, except I am OK with ASTM A53 Schedule 80 pipe rather than A106 Schedule 80.

The codes allow the A53 pipe, which comes either as ERW (Electric Resistance Welded) or seamless. The A106 material is always seamless, but cost is 3x to 4x more than the A53.

Choose A53 or, if you can afford it, A106, either specification is OK for our small steam plants, but do use a minimum of Schedule 80 for all boiler attachments, as well as 300 LB rated fittings.

[DetroiTug]

Oh ok, I wasn't aware of that. Sch80 A53 is ok for piping too. I recall in the case of boiler shells, A53 was ok, but the seam had to be Radiographed and certified. I assumed they used the same level of caution in the piping.

-Ron

[cyberbadger]

I agree on the schedule 80 piping.

But what's wrong with say for example a quality Class 150 Ball Valve from Mcmasterr Carr for a MAWP of 95PSI? (Model 47865K23)

-CB

[DetroiTug]

Yeah, it looks like that would work for less than 150 psi. That is the first time I've ever seen those on there, they must have just started carrying them. Before it was CWP type not rated for steam and 250psi/406 degrees.

-Ron

[fredrosse]

Yes, another important point, Valve Ratings. The typical valves available will have packings and sealing discs of various materials. Some are good at low temperatures, some will fail at steam temperatures. In general, typical valves bought in the USA are marked with the intended service:

"CWP" this means "Cold Water Pressure", with no assurance it will be OK for steam service.
"WOG", meaning "Water, Oil, or Gas", again no assurance it is OK for steam service.
"SWP", meaning "Steam Working Pressure", indicating the valve is rated at least for the saturated steam pressure / temperature.

Often valves cary dual ratings, my feedwater isolation valve is marked "600 WOG" as well as "150 SWP". If you get a valve that does not have these markings, then look them up with the valve model number on the manufacturer's website, or call them. If they only speak a far eastern language, then get a translator!