Two Pipe Thermostatic Trap - water hammer

David_11

This past year a new boiler has been installed in my residence, replacing the original 1920 boiler. Original system was a Mouat two pipe vacuum steam heat system. For the past few months the system has worked well - you did not even know the system was operating. Since this last bit of cold weather in Cleveland Ohio after the holidays there is water hammer occuring at three of the eight radiators in the house - although only at start up of the boiler - once the air has left the system from the F&T trap in the basement the hammer stops and the radiators get warm, not really hot. From this I understand the Thermostatic Trap has failed or is in need of replacement. Water is dripping from one trap during the heating cycle!

The question I have relates to the type of thermostatic trap at the radiator. The system still has the original trap at the radiators with name Mouat embossed the side of the device. It appears to have worked for the last 80+ years. If indeed the trap has failed what type of trap should be used to replace the original 1920 part or is the original part able to be cleaned / repaired? I am getting all kinds of different solutions from Contractors that contradict each other or is there no one really specific trap for this type of heating system?

Really confused - if anyone is able to help I would greatly apprecriate the input.

Thank you.


David Schelhorn

Steamhead

Those may not be traps

they may be water seals. These have zero moving parts. If they're about an inch in diameter or so, they're water seals.

Sounds to me like the problem is in the basement and the sound is echoing into the radiators. Has anything changed down there? Maybe the F&T trap is plugged and water is backing up in the main.

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gerry gill

sure I'll help,

first there are several Mouat traps out there..one style is just a water seal trap..next is what we call an outboard trap, it sits sideways..there are at least two types of these..one has raised letters that says august 1929 on it..the other just has a metal tag thats usually painted over...and there is a newly discovered trap that sits in normal fashion and says Mouat-Squires on it..these are from the 30's after tom mouat sold the business to squires heating...okay...next...you wont find a replacement that ''fits right in'' for any of these..any trap can be made to work but some piping alteration may be necessary..we have been ordering replacement cage units for these outboard traps from Barnes & Jones company..basically its new guts with a new cap..so far they work well..but if you have the original mouat valves on the radiators then you should not really ever get steam to the other end..mouat would have his guys set a maximum opening position on the valve and it could not travel past this point..the whole trick to mouat is to vent the return massively...and BALANCE every radiator...of course this means every radiator valve must work..and boiler firing rate and pressure is critical..i'm in bedford ohio by the way..feel free to call..I work on more Mouat systems than anything else..440-439-4417..gill plumbing and heating..a steam buddy Steve Pajek and myself have a steam laboratory over on lincohn street cleveland heights that we experiment with..its also a mouat system..currently we have a german staged gas valve on the boiler and no mechanical vents..its mimicing mouats coal boiler nicely..Mouats systems were really quite simple but take alot of tweaking/balancing..they are also one of the best systems ever made..also I hope your definition of f&t trap is different from mine.