Inverted bucket steam trap

[gatossi]

Good day! I'll need your help with steam traps.

I've been asked by our process guys for a steam trap for which the line's design conditions are:
Press: 30 kgs/cm2
Temp: 330 ºC
But (always a but!) they recon the line won't see that much pressure constantly... on the contrary... it is going to be much lower.

Their cuestion was: How little the pressure should be to assure that the (inverted bucket) steam trap will work? (without having a long steam column on the line)

I've done my homework and checked the vendor (Armstrong) and they said that it will be 5 psi (0.35 kg/cm2) but that is just what the datasheet says... so I'm wondering if you guys could bring a bit more light on this!

Thanks!

 

[katmar]

What do you mean by "to assure that the steam trap will work"?

If you are talking about sealing when there is no flow then an inverted bucket will seal better at low pressures than at high pressures because the lower steam density makes for more bouyancy.

But if you are talking about getting sufficient condensate through the orifice then I would go with the Armstrong spec sheet. They have been around a long time and have an excellent reputation. I don't see any reason to doubt them.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[gatossi]

Sorry, i wasn't very clear on that point.

Process worry is: with a very low pressure on the line, how long (big) will be the column formed by steam before it really makes the steam trap work?

 

[katmar]

I'm confused by your "column of steam". All the steam you need to get the trap to seal is to displace the liquid trapped in the inverted bucket. This will be very little.

If you are talking "column of steam condensate" to give the required pressure then 5 psi is about 2.5 feet of water column, neglecting any actual steam pressure or back pressure on the trap.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[gatossi]

Katmar, that is exactly what I meant... thanks!

 

[katmar]

Whoops - major error. Sorry gatossi, 1 psi is 2.3 feet of liquid so 5 psi will be about 11.5 feet of condensate column.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[ApC2Kp]

gatossi,

Any steam trap must be capable of containing the steam at supply pressure, 30 kg/cm2 for your application. The body rating might be PN40 (ANSI CL300).

Operating mechanisms for inverted bucket traps have a limit of the pressure that works against the valve seat area. The weight of the bucket and mechanism needs to open valve against the force of steam pressure acting on the orifice seat. The orifice seat diameter could be larger to allow more flow for the lower pressure applications. For the higher pressure applications the orifice seat diameter will be smaller for the weight of mechanism to operate yet have adequate flow driven by the higher steam pressures.

The optimum sizing of the steam trap is a choice of orifice seat size that provides the capacity at expected pressures, but will operate at full steam supply pressure. If you study the capacity rating charts for the inverted bucket traps, there are flow ratings for each orifice size that have a limiting peak. Each succesive smaller orifice has curve to show flow rating for next higher range steam pressure.