one pipe steam boiler short cycling

bennybuff

we recently had trv valves installed on all the radiators in a 6 floor 100 unit building and now the boiler towards the end of each cycle starts to short cycle. what should I be looking for ?

Fred

What is the Pressuretrol/Vaporstat set at? Do you have adequate venting on the Mains? You need to vent them fast. How many radiators are on the 6th floor? what % is that total relative to the other floors? It is quite possible that enough of those radiators are staying closed, as a result of the TRV's that the boiler is now essentially oversized for the remaining radiator EDR. TVR's are great for some control in a room or two but when used across a good portion of a house house (or in this case a good portion of an apartment building) that is likely to be to much, especially if the boiler is oversized or the Main venting is inadequate.
You may need to replace some of those trv's with slow radiator vents to reduce the steam flow through those radiators but not completely close them off which is what a TRV can do.

KC_Jones

Once the TRV in a room is satisfied it closes and doesn't allow any more steam in. That radiator is now effectively removed from the system and makes the boiler over sized. Once a bunch of TRV's are satisfied it gets compounded. Once the boiler is effectively over sized it will build pressure faster and short cycle on the pressuretrol or vaporstat as the case may be.

KC_Jones

Not directly related to your question, but relates to your system. Here is an interesting article about a large system with all TRVs.

http://www.fiainc.com/documents/10-08Canyoureallycontrolaone-pipesteamsystem.pdf