F & T steam Trap PSI rating

michaelmiracle

I have just taken over the maintenance for a school in Denver built in 1924. The previous caretaker was here 10 years and said he never changed the steam traps. The piping system is a 2 pipe original to the building. There are 40 radiators on 2 floors and a basement which mostly gets heated by the piping that runs through it.
I am changing all the steam traps this summer assuming they are all finished. In the basement there are 4 F&T H traps. 2 are rated 15 psi differential, 2 are rated at 75 PSI diff. I'm getting all of my replacement kits on eBay as new old stock. It is much easier to get 15 PSI then 75 PSI, and cheaper. 2 of the F&T traps were put in upside down and sideways so I don't have much faith that everything was done right in it's 100 year history.
Question: Is it critical to have 75 PSI traps replaced with the same rating? Is there any reason that in the same system there is this discrepancy between ratings? Can I just replace all 4 with 15 PSI kits?

EBEBRATT-Ed

The trap differential is the difference between the steam pressure at the inlet to the trap and the pressure if any in the condensate return.

Not all traps have the same rating. So a Hoffman 3/4" trap rated at 15 psi may have a very different rating in LB/hr capacity than say a Barnes and Jones trap. You have to look in the mfg spec sheets.

A 75lb trap say 3/4" will have a much smaller orifice in it that a 3/4 trap rated at 15psi. which will reduce the capacity of the 75lb trap when used on a 15 psi system.

Using traps rated higher than the system pressure/differential is ok as long as you allow for the lower capacity.

You should never use a trap on a system rated higher than the traps differential pressure

So the first thing to find out is the system differential

michaelmiracle

is the differential just what I set the pressuretrol at or is there a formula to figure it out that I can use? The system pressure as it is set now is 2 PSI and a 1.5 differential at the pressutrol.

DanHolohan

Use 15-psi traps everywhere. 

Mad Dog_2

Very good chance, the last installer just used what supply house had on the shelf in the back.  Mad Dog  🐕