steam return vents

srd357

Hello Everyone

Got a customer that has a small, 8 radiator, 1 pipe steam system.  The return vents are 3- number 4 Hoffmans, which I'd like to replace.  My supplier says that Hoffman 4A is the same vent and wants to sell me them.  My research says that they are not the same.  First, are the existing number 4s the correct vents? If not, what should they be?  And second, is the supplier correct?



Thanks Steve

Rod

Yoiu need Bigger Main Vents

Hi Steve-  The Hoffman #4 is a thermostatic vent which doesn't have a float to stop water escaping.  The Hoffman #4A does have a float. These are going to be used as main vents, correct?

If you look at the venting capacities of these vents compared with the main vents normally used on residential steam systems (Gorton #1 & 2 , Hoffman #75) the vents used now  have a very, very small venting capacity and this has to be affecting the performance of the steam system.

 As you can't "over vent" main vents, you would be far better off replacing the present  vents, at a minimum, with Gorton #1 s which have 5 times the venting capacity of the vents you are using now. The system should then get steam to the radiators a lot faster. If you can get back to us with the size pipe and length of the mains we can then calculate how much venting you need.

- Rod



Per Gerry Gill's excellent venting chart the following shows the venting capacity at one ounce of steam pressure. As you can see the Hoffman # 75 and the Gortons are have much bigger venting capacity to what the system has now.



Hoffman #4      0.060  cu.ft. per minute

Hoffman #4A    0.133  cu.ft  per minute

Hoffman #75    0.500  cu. ft. per minute

Gorton #1        0. 330  cu.ft. per minute

Gorton #2         1.100  cu.ft. per minute.

srd357

steam vents

Hi Rod.   Thanks for the info.  There are 3- 2" supplies, each goes about 20' to the last radiator.  Then, still using 2", returns back to the boiler. At this point, are the Hoffman#4s.  If precise measuring is needed, I can do that.

Thank you

Steve

Rod

Main Vents

Hi Steve - Again using Gerry Gill’s excellent venting book, one lineal foot of 2 inch pipe contains 0.023 cu. ft of air.  A 20 foot main contains  0.46 of a cubic foot of air.  A 20 foot plus a 20 foot return contains 0.93 of a cubic feet of air.  Using a Gorton #1 @ .330 cu.ft of air a minute this would mean that steam would theoretically reach the end of the main in 1.39 minutes and the end of the main in about 2 3/4 minutes.

                                                           End of main                      End of Return

One each Gorton #1 per main -             1.39 minutes                     2  3/4 minutes

Two each Gorton #1s per main             0.695 minutes                      1.39 minutes



One Gorton #2 per main                         0.48 Minutes                     0.85 minutes



Using the old vent

One Hoffman #4  @ 0.060                       7.6 minutes                      15.3 minutes



Using a Hoffman 4A vent:

One Hoffman #4A @ 0.133                       3.4 minutes                       6.9 Minutes



I would use a least two Gorton #1s on each main or perhaps even one Gorton #2 on each main.

As you can see either setup would greatly reduce the time it takes to get steam to the radiators which should show a dramatic improvement in the system.



I use the Venting Book practically all the time and if you're doing steam systems I highly recommend it.  It’s available in the Shop section of this website as a downloadable E- Book and it is also included as part of the book, “ Greening Steam”.  Here’s a link to it:

http://www.heatinghelp.com/products/Steam-Heating-Books/25/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

- Rod

srd357

steam vents

Thanks, Rod