Lifting condensate

kszyho100:

The way you have worded and written your query doesn't reveal that you understand the mechanism or action of a steam trap. Therefore, in order to help you with a positive response, I'm going to revert to some steam trap basics.

A steam trap is a mechanical device that automatically segregates, on a continuous basis, the two phases created in a saturated steam environment - the vapor phase and the liquid phase. It does so by expelling the liquid condensate phase using the vapor pressure existing in the condensate collection chamber. This vapor pressure is related, of course, to the primary steam pressure supply. Therefore, depending on the type of steam supply control you employ, you will have a positive vapor pressure to force the condensate out of the steam trap and into your condensate collection system. If you have condensate formed in a steam supply header, the driving force available to expel the condensate (and "lift" it to a height) is the vapor pressure existing in the header. If you have a float-type of steam trap, the principle is the same if you maintain your condensing system pressurized at the header pressure. However, if you are using a control valve to throttle steam feed to a condensing device then you have a different, lower pressure existing in your condensing chamber and will have less driving force.

Without knowing any more basic data, you have, in my opinion, no reason or basis for inserting a check valve downstream of your steam trap - if that is what you mean by "after". The check valve serves no purpose in that location since the pressure downstream of it normally is always less than the steam vapor pressure upstream of the trap and flow in the contrary direction is not possible since the driving force is negative. All the check valve does in this application is give you additional pressure drop and problems - besides the initial cost and maintenance expense.

Condensate flow downstream of a steam trap should always be assisted with sloped piping, whereever possible, and without any dead legs or "pockets" in the piping. I don't understand what you mean by "it is possible to lift condensate only once". I can lift any fluid any quantity of times I so desire - as long as I have a driving force I can apply to it.

I hope this helps you understand what is happening in a condensate trapping and collection system.

Art Montemayor
Spring, TX

Consider and ponder the complications resulting from condensate partial flashing into steam, in particular when dealing with lifts.

I may have probably posted my message just after Art Montemayor's, thus I couldn't have known of its contents. My intention was to make kszyho100 reflect on her/his design.

Anyway..., putting the check valve after the trap would probably mean the designer's intention was to protect it from the hammering forces that may develop from condensate's partial flashing into steam.

As for the syphon-like arrangement intended by kszyho100, if that is what was meant in the first place, let her/him think on the effects steam bubbles, collecting on high pipe turns, might have.

Besides, the friction drop on a horizontal and vertical two-phase flow may be higher than the envisaged lift-plus-liquid-friction-drop may indicate.

I still consider kszyho100 should think matters over and probably read a tutorial on the selection and installation of steam traps, and design of condensate collection piping, as can be found by a quick Google search.

This link to the leading UK manufacturer of steam products and applications might help