Oversized steam traps?

[david6245]

Hello,

I am pondering the consequence of oversizing a steam trap. I can understand why an undersized steam trap would be problematic, i.e. backing condensate into your steam header. But what would an oversized trap do? Release steam?

Any light shed on this subject would be appreciated.

 

[rmw]

What kind of trap are you considering using? I might answer differently depending on your trap type.

rmw

 

[david6245]

Our site has been moving towards free float traps. I have seen a fair amount of inverted bucket traps as well from older installations.

I am specifying traps for steam tracing as well as drip lines in steam mains.

Any help would be great. Thanks,

 

[katmar]

The losses through a trap are more-or-less independent of the flow rate, but are larger for large traps than for small traps. So if you use an oversized trap your losses will be more than if you had a correctly sized trap. Your trap supplier will be able to advise you on hard numbers, depending on the style and size of the traps.

Also, large traps cost more than small traps so it will impact on your capital cost, especially if you use larger piping and valves to match the larger traps.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[david6245]

katmar,

I was referring more to different orifice sizes within a trap of the same body size, say a 2" trap. If, for that 2" trap, I have a choice of several orifices with discharge capacities ranging from 400 lb/hr to 2,500 lb/hr for a differential at 250 psi, and I calculate a condensate load of 500 lb/hr (with safety factor), what would be the consequence of having an orifice that can dishcarge 2,500 lb/hr when all I need is 500 lb/hr?

I may be splitting hairs here, but I am relatively new to this I want to be sure I understand.

Thanks again,

 

[katmar]

OK - disregard comments on costs.

But larger orifices still mean larger losses. This may or may not be significant. If/when a trap fails open then a large orifice of course wastes much more steam than a small orifice. For particular information on your traps call in your sales rep. Steam trap reps generally have a very good reputation for technical assistance.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[ApC2Kp]

david6245,

The inverted bucket traps could operate on higher pressures with the smaller orifices. The IB mechanism has weight to pull the valve open away from the orifice seat. Larger sized orifices of IB traps have less ability to open the valve against the steam pressure. So it would be better to select the smallest orifice size of IB trap to get required capacity for condensate flow, and avoid IB trap lockup due to overpressure on the valve to orifice seat.

If it were a thermodynamic type steam trap like small disc traps used on tracing lines, the oversized capacity traps would cycle more frequently resulting on wear and premature failure. The disc traps typically fail open, so there would be steam blowing through and consequently wasted steam. One manufacturer offers an insulation cap for their disc trap to shield it from cold wind, which would also cause it to cycle excessively.

 

[ione]

David,

Take a look at the link below there’s a wealth of information.

http://www.spiraxsarco.com/resources/steam-engineering-tutorials.asp#block11

I can’t see other detrimental effects on using oversized steam traps but those mentioned by katmar.