Multiple kind of main air vents

andyz

I have a 2 pipe gravity return system, (no radiator vents) there a two long mains which come to an end on the far side of the basement and drop down into a hartford loop or at least a wet return. At the end of the mains are air valves. One was a Dole Quick Vent #5 and the other a Dole Model 90.(above the boiler on the return is also a Hoffman Main Vent Valve #75).The Dole #90 recently failed and was replaced with a simple Dole #4.Question: should these 2 end of main vents be the same, is the Dole#4 OK, the old Dole you could hear sucking in air when the boiler cycled off, but these 2 are now silent. The Main#75 vents when the boiler fires, every thing works fine, just wondered what the difference is?

jpf321

was going to...

i was going to recommend that you get Mr. Gills book http://www.heatinghelp.com/products/Books/5/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek .. but in looking at it, I see that it doesn't list the capacities for all the vents you mention .. it only has Dole #5 and Hoffman #75. 

Jamie Hall

There's no harm to mixing

vent sizes or makes.  And if everything is working... "if it ain't broke...!"