blow down

[johnp]

is it ok to use 400 degree silicone heater hose for the connection to my blowdown thru hull?

[Chris W]

I'll leave the application advice to those with greater knowledge but will say that if you use silicone hose, make sure you use the proper type of hose clamp. The typical worm gear clamp has perforations that the silicone hose will extrude through before it is tight enough to stay on the fitting. Some clamps have a flat band that fits between the hose and perforations preventing the extrusion but the best clamps for the job are made by AWAB. They cost more and are worth every penny.

[Lopez Mike]

My blow down piping is all steel as it discharges above the water line and clears the gunnel slightly. No hose involved.

My question is this. How large should the blow down piping and valve be? I have a 33 square foot VFT and the boiler penetration is 1 1/2" as is the quick opening valve. It then necks down to 1 1/4" for a couple of feet.

This seems large to me. I have worked on a full sized locomotive where the blow down valve opening was only 3".

I'd like to hear from others on this. (sorry about hijacking your post!)

[fredrosse]

Hose for blowdown service should be rated for both the temperature and pressure of the steam blow. Having silicone hose, which is good for 400F, in no way implies that it is good for steam blowdown service. Obtain both the pressure and temperature rating for the hose. Steam pressure rated hose is available, and stainless steel bellows flexable connections, with stainless steel outer braid is often rated for this service.

[barts]

I have a length of regular steam hose that I've used for blowdown. It is connected to the boiler, but the other end is free. The length is sufficient to reach over the gunnel and into the water if I want to blow down quietly. This is also handy when draining the boiler on the trailer as it is long enough to form a siphon and get the last bit of water out even when the boiler is cold.

- Bart

[DetroiTug]

I've been using Marine exhaust rated hose for blow downs, and it works, but I'm changing them to stainless steel braid and hard pipe.

Also, the rigid piping from the relief valve to the roof and the whistle line to the roof are getting a stainless steel braid to take the load off the piping at the boiler connections.

-Ron

[farmerden]

I just used washing machine hose as one end is just held over the side.This is just a temperary measure til I plumb it properly-The trouble with temperary-Oh lets see how long have I owned the boat? Mike I would make the outlet as large as possible. When I cleaned out my muddrums this spring I noticed some scale in there that, I don't think would pass thru smaller valves ,but maybe the crud gets mashed down by the steam pressure.As for the washing machine hose wear gloves -boy does that pipe get hot quick! I think I would still use a flexable hose but I wonder if it only has to be temperature rated as it really is an open exhaust line not a pressure line. Den

[barts]

Well, I'd be careful. Washing machine hose isn't exactly rated for either 350 F or 150 psi...
suddenly holding a lot of steam in your hand isn't that fun.

- Bart

[artemis]

Yeah, particularly if a big piece of that scale plugs the hose at a bend. Wonder what the exploding pressure/temperature of washing machine hose is?

[fredrosse]

I wouldn't recommend it, but if you are going to use washing machine hose, use rubber, not plastic, and definately use stainless braided hose. It costs a little more, and is available almost everywhere with the stainless braid. But, as Bart says, a blown hose can spoil the day.

In a previous life I did much analysis of steam/water blowdown characteristics, and when blowdown hoses have saturated hot water entering them (thru a valve that is the same size as the hose), pressure stays up close to boiler pressure throughout most of the hose. This is because a small reduction in pressure across the valve allows the water to "flash" into a steam/water mixture, and the steam volume is many times the water volume, so velocity increases, providing plenty of pressure drop to keep most of the line pressurized.

And, as Ron points out, when something lodges in the hose, full pressure exists up to the obstruction.