Weather Cover/Chinese Hat

[psafety]

I've researched everything I can find to no avail concerning deltaP related to the effect of a weather cover on a vertical relief line. I think at one point in the past I had seen an estimation based of % free flow height (above pipe exit) as related to diameter.

Does anyone have a reference, or could point me to one?
Don

 

[MJCronin]

psafety,

I have only seen "chinese hat" rain covers on flue gas vents (stacks)from boilers, never on safety or relief valve discharges.

Addtionally, unless you have a very large amount of rain and/or no means to drain the flue gas vent, I would recommend against these.

If you have a safety/relief valve dischrge, put a drain on an elbow inside the building and you are done.

-MJC

 

[FILGUEIRAS]

psafety,

in addiction to the drain suggested, your vent may be covered with a light, loose lid ( attached by a string, to avoid beeing thrown away ). If the line doesn1t have constant flow, this will avoid any unexpected clogging.

 

[psafety]

I was asked this question last week, in relation to venting an indoor tank. The material is such venting indoors is not preferred.

Typically, I use two 90's to make a "goose-neck vent", but this question arose, thus my enquiry.

 

[zerosum]

Slip the next larger size concentric pipe with spider support arrangement over the (outside) vertical vent, drill a ~3/16 at the low point in the vent system (preferably outside the building). The top of the larger pipe should be a couple of diameters above the smaller to deflect the rain. Very little rain water will enter the actual vent, and can drain out the hole.

Chinese hats are to be avoided.

 

[dcasto]

I use a "sock" that is water proof to cover relief vents. They are sold in safety catalogs. They cover the vent and keep water out. They are usually bright orange so you can see your vents easily too.

 

[BigInch]

Zerosum, I personally don't like the idea of a larger pipe slipped over the smaller, unless you like launching things into near earth orbit.

There seem to be pleanty of uncovered vents around with a 1/4 inch hole at the bottom of the ell coming off the PSV outlet for draining any accumulated condensation or rainwater.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[zerosum]

Biginch, maybe my exposition is not too clear. I was proposing concepts as in ASME B31.1 Appendix II (Rules for the Design of Safety Valve Installations) or the American Conference of Industrial Hygenists Stack Head Design (Fig 6-24 in my version) of that manual. I think the chinaman's hat version is a lot more likely to launch than a concentric (open both ends) pipe version of a rain suppression attachment.

psafety, the latter reference ACGIH manual does provide in several places the estimated loss due to 'weather caps' along with a warning in each place 'not reccommended' or 'wrong'.

I used very successfully a few years ago a 'rain tripper' and drain arrangement shown in the offset stack of Fig. 6-24. Looks to me like there are a couple of good concepts there in that figure to deal with your problem.

Probably the cheapest solution is dcasto's suggestion. Unfortunately, it would never, ever fly in our operation.