Blow Down Pressure

[JonRiley56]

Hi All,

I had the boat out again yesterday afternoon for a bit. Had a few challenges, but overall it was OK. I have only steamed it three times so far. I will likely get out a couple more times before the snow flies. I have yet to blow it down since it has had so little activity. What pressure should I let it drop too before I blow it down? Do I need to be concerned about its temp following blow down ? I am assuming that if the pressure is coming down steadily on its own that I dont need to be overly concerned.

If I am laying up for the winter do I go ahead and blow it down completely as opposed to just enough to remove sediment etc ? I know that Fred has a way to "boil off" any remaining water in the system after he drains it by pulling a vacuum, but that is beyond my pay grade. I was figuring I would blow it down all the way and then build a small fire while I run aire through it to dry it out. I will drain all the lines separately.

I look forward to your thoughts.

jon

[gondolier88]

Remove all traces of a fire and allow the boiler to drop to between 20-30psi, with about half a gauge of water showing if you want to clean the boiler as well as drain it.

As you say, temp. is directly linked to pressure, and once you have blown all the pressure out of the boiler it will lose temp. very quickly, however, if you have a fusible plug make sure all traces of your fire are removed before emptying it as you could weaken the plug.

After blowing down to 0psi, shut the blowdown and make an opening at the top of the boiler that will let any residual moisture evaporate (ie. remove a safety valve or whistle valve etc.) And make sure you have removed all traces of the fire before you make an opening.

I hope with the above you are now not considering making a small fire in your now empty boiler- a boiler is designed and stressed to cope with a temperature corresponding to it's working pressure, not for localised high temp. heating (even if it is a small fire!)

Once blown down, leave the boiler open at the top, and ideally remove a fitting close to the foundation ring, place a low temp. heat source in the firebox (such as a 100w greenhouse heater or a 100w light bulb) and allow a circulation of dry slightly warm air through the boiler.

Another way is to completely seal the dried-out boiler and place lime or silica crystals inside to absorb any small amounts of moisture inside.

Greg

Oh, and make sure you remove all traces of a fire first!!!!

[fredrosse]

I agree with gondolier88 on this method.

Also, if there are sections of your piping that cannot be properly (fully) drained, this piping should be opened up and blown out with compressed air. My blowdown connections have an undrainable loop, and I pressurize the empty boiler with 100 PSI compressed air, then open the blowdowns which removes virtually all the water in these lines. A few days drying with a heat lamp in the firebox, stack plugged, and boiler upper/lower connections open will allow boiler dryout.

Another option is to use some RV Antifreeze and fill the piping. I disconnect the boiler feedwater inlet connection, put RV antifreeze into the feedwater tank, then work the manual feed pump until the pink antifreeze comes out, then I do the same thing with the engine driven pump, running the steam engine on compressed air (or a vacuum pump connected to the exhaust line) until all those pump passages are filled with the antifreeze.

One other issue is the loop seal on pressure gauges. These pocket water, and there is no way to empty the loops unless the gauge is taken off (for storage in your heated den), and then the loop is blown out with compressed air.

[steamdon-jr]

John, I am assuming your are talking about full blowdown which everyone has sort of already answered well. I also like to blow down the boiler and the gauge glass at least once per outing even more if I am on dirty water like a river after rains. I do this with full pressure around 100 PSI and I usually start with a full glass and blow off a 1/4 to 1/2 glass and then shut it down. when I blow down the glass I close bottom valve and to boiler and open drain forcing all pressure thru top valve, then I open bottom and close top and repeat...this assures that the small orfices on the gauge glass are not blocked with scale or sediment which could make for a very bad day if you have a false reading on your glass.

[fredrosse]

steamdon-jr is correct in blowing down the boiler for general sediment control on every outing, and blowing down the sight glass frequently.

Blowing down the sight glass can be done at any pressure, from about 15 PSIG to full operating pressure.

The recommended sequence is as follows:

1. Shut the lower sight glass valve
2. Shut the upper sight glass valve, then open it just slightly, about 1/4 turn.
3. Open the sight glass blowdown valve, the upper valve will push the glass water out, and flush away the water and some dirt.
4. Open the upper sight glass more to clean the glass if necessary, then return to the slightly (1/4 turn) open position.
5. Slightly open the lower sight glass valve, this will admit flashing water into the lower gauge region, and more dirt/mud will be blown out.
6. Close the sight glass blowdown valve, water will fill the glass up to boiler water level, and it probably will be muddy. If it is muddy, then open the blowdown valve again and blow out the muddy water.
7. Repeat step 5 until the water becomes relatively clean/clear.
8. Finally close the blowdown valve, then fully open the lower sight glass valve, then fully open the upper sight glass valve.

This sequence keeps the upper glass valve open somewhat throughout the blowing operation, and avoids the potential of “waterhammer”, which can sometimes break a sight glass. Breaking the glass doesn’t happen often, but when it does it is sometimes a real inconvenience.

[fredrosse]

Blowing down for sediment control can also be done at full operating pressure, but I prefer to do this when there is only 15 to 30 PSIG in the boiler.

Inside an unfired boiler (but hot and pressurized with steam), the steam, water, and metal surfaces are all at the saturation temperature. When pressure is vented from the boiler, the saturation temperature goes down, and the remaining water flashes into some steam, the water in contact with the metal surfaces pick up some extra heat, and generate some more steam.

These steam bubbles generated during blowdown create turbulence, stirring up the sediment that has settled in the boiler, and that is the stuff you want to get rid of. The volume of steam bubbles emanating from a hot metal surface is about 5x larger when this process occurs at 15 PSIG as compared to 150 PSIG, (the volume of a steam bubble of any mass is inversely proportional to the absolute pressure) therefore more turbulence and more stirring up the sediment. I also use portable stainless braided flex hoses for blowdown, and trust these hoses more at 15 PSIG, I would be fearful of these hoses with 100 PSIG blowdown.

[JonRiley56]

thank you all !!!!!

jon

[Lopez Mike]

Don't overlook the possibility of using a wet or dry vacuum for getting water out of piping during Winter layup. Between a complete boiler blow down, sucking the hot well dry with the vac and sucking the pipes dry, I can stuff a drop light in the firebox and go read steam books for the Winter.

Mike