Pressure Relief Valve Question

[JonRiley56]

Hi all,

I have been looking at pressure relief valves for my system, and while it is easy to find the pressure they are set to lift at, I cant find anything about how long they stay open and therefore how much steam will be lost. I am looking at the Kunkle 6010 set for 150 psi.

I would greatly appreciate any help.

jon

[DetroiTug]

Hi Jon,

I had the same dilemma looking for a relief valve and wound up with a 10% let off. I would have rather had a 5% valve. It's really only an issue dockside, under way it never reaches blow-off.

These folks here have tech's you can talk to:

http://www.boilersupplies.com/

McMaster-Carr does as well, and they can get about anything.

-Ron

[JonRiley56]

Hi Ron,

Thanks ! I assume that I should go with a valve that has openings that match those on my boiler, or are bigger rather than necking the opening down to the valve ?

Also, did you put a drip tray elbow on yours with an up pipe to direct the blowoff away from the deck ?

I will send you a picture one of these days, in the dark, in a driving rain.............I am embarrassed by my measly efforts compared to what you guys do...........ah well..........you have to start somewhere I suppose.

jon

[DetroiTug]

Jon,

Others here can probably answer this better, but yes the relief valves' inlet should be the same size. They are typically one size pipe larger on the exhaust side.

I connected this one with a street El at the boiler and a street El on the exhaust pipe which is 3/4" and that goes through the roof. I'm going to add a braided flex line on it and the whistle pipe that is attached in the roof, I don't want to have any piping subjected to the mass and inertia of the boiler or supported by the boiler. i.e. piping that is mounted rigid on the end away from the boiler. While trailering etc, the boiler may want to flex in it's mounting, this should put no load or strain on any piping.

As Ron Fossum said, if it floats and moves under it's own power it's a success.

-Ron

[fredrosse]

Three relevant points for the safety valve:

1. Set Pressure, Valve must be set at or below the MAWP (Maximum Allowable Working Pressure)

2. Valve flow Capacity, the valve must have a flow passing capacity greater than the steam generating capacity of the boiler.
There has been discussion of this within this forum, however most of our small steamboat boilers need only the smallest ASME safety valve Kunkle makes, 1/2 inch IPS. The 20 square foot surface area boiler for Margaret S. needs a safety valve capacity of 108 PPH (Pounds Per Hour), and the valve is rated for over 300 PPH, the smallest valve manufactured by Cobranco.

3. " Blowdown", the steam pressure reduction at which the valve reseats after popping open. About 10% is typical, however the valves can be adjusted for another amount, as Ron says, a lower amount might be preferred, but usually not a big issue.

An ASME Code approved safety valve is fitted with a seal and lock-wire to indicate if the valve's settings might have been tampered with. This is attached to the valve and assures the settings match the nameplate on the valve. All valve manufacturers have tables listing the valve capacity vs. steam pressure for a standard set of valve discharge orifices and valve stem lift, and operating pressure. An acceptable valve installation requires no other valve whatsoever in the safety valve inlet and discharge piping, no piping smaller than the safety valve's connection sizes, piping as short and direct as possible, and the safety valve stem mounted vertically upward, with no excessive stress on the piping and valve body.