2000 Hook-up Book

Draining Temperature Controlled Steam Equipment

Closed Loop Drainage Systems

Float and Thermostatic type sized not for the equipment load, but to handle the high flow rate during the brief pump discharge period. The trap must be capable of handling the full system operating pressure with a capacity of stall load at 1/4 psig. This size trap will allow the pump to operate at its maximum capacity. Multiple Parallel Coils With A Common Control Valve While group trapping should gen erally be avoided, a system with a single control valve supplying steam to identical parallel coils within the same air stream can be drained to a single pump/trap combination closed loop system. (See Fig. 47.) This hookup requires that the pressure must be free to equalize into each coil. No reduced coil connections can be permitted and the common con densate manifold must not only pitch to the pump but be large enough to allow opposing flow of steam to each coil while conden sate drains to the pump/trap. The basic premise still applies, that coils which are fully air vented and free to drain by gravity give maxi mum heat output.

With pressurized returns and larger coils, it is often economical to fit a combination pump/trap to each coil in a closed loop system rather than the conventional grav ity drain line accepting condensate from several traps and delivering it to a common pump. The pump/trap system is illustrated in Fig. II-35 (page 101) with the check valve fitted after the trap. This hookup assures maximum heat from the equip ment and provides the additional advantages of no atmospheric venting, no vacuum breakers, therefore less oxygen contamina tion and no electric pump seals to leak. Integral to the design of this system is the air vent for startup, the liquid reservoir for accumula tion during discharge, and consideration should also be given to shutdown draining with a liquid expansion steam trap. Sizing A Combination Pump/Trap The Pressure-Powered Pump ™ selected must have capacity to handle the condensate load from the equipment at the % stall con dition. Trap sizing is more critical and should be a high capacity

SYSTEM DESIGN

To make equipment drain by gravity against back pressure, the steam trap must be replaced by a Pressure Powered Pump ™ or pump/trap combination installed in a closed loop system. In this arrangement, the equipment does not have a vacuum breaker but is pressure equalized to drain by gravity, then isolated while condensate is pumped from the system. The basic hookup is shown in Fig. II-32 (page 99) where the equipment is constant ly stalled and back pressure always exceeds the control valve supply pressure. In many closed loop applica tions, the pump alone is not suitable because the steam sup ply pressure can at times exceed the back pressure (P 1 is higher on the “Stall Chart” than P 2 .) These applications require the Pressure Powered Pump ™ to be fitted in series with a Float and Thermostatic trap (combination pump-trap) to prevent steam blowthrough at loads above the stall point.

Before

After

Steam Control Inlet

Steam Control Inlet

Steam Control Inlet

Steam Control Inlet

Air Vent

Air Vent

Steam Coils

Steam Coils

To Condensate Return

Steam Coils

Steam Coils

Air Vent

Air Vent

Air Vent

Air Vent

High Pressure Drip Traps

Reservoir

Motive Steam

Motive Steam

To Condensate Return

Level-Control Drain Tank

To Drain

Pressure Powered Pump/Trap

Figure 47 Combination Pressure-Powered Pump/Traps in a Closed Loop Eliminate Waterlogging in Parallel Steam Coils Previously Trapped to a “Stalled” Level Control System

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