Steam Basics - Steam Trapping - In the Beginning
The first method used to control condensate discharged was hand operated. An
operator would use a hand valve positioned on the discharge line reducing
or increasing flow. While this was considerably better than an open
discharge line, it was still quite difficult to determine if the valve is
open just the right amount. The valve wide open would lose valuable
live steam; if not open enough condensate will back up filling the steam space. In
addition, any change in the rate of condensate forming or change in steam
pressure also causes the loss of live steam or the backing up of condensate,
whichever may be the case. In all cases, there is substantial efficiency
loss.
Another early method of controlling condensate flow was to fit a
plate or disc with a hole or orifice in the center and simply insert this in the discharge
line from the apparatus. To correctly size the orifice you must first
calculate the condensate flow, based on the condensing rate of the equipment. Knowing
the pressure at the orifice, the required size can be fitted from an orifice
flow table. The orifice plate is a very efficient device when correctly
sized and condensate line operating conditions remain constant, but steady
operating conditions happen very infrequently. When condensate flow rate
or pressure vary, the orifice selected is no longer the correct size and will
either back up condensate or blow live steam. An automatic device was
necessary to let the condensate out, but hold back the steam, and this led
to the development of today’s wide range of steam traps.