STEAM TRAPS Introduction Steam Trap Selection Guidelines • DRIP Applications
DRIP Applications • Sizing a Trap for Draining a Steam Main
Drip applications refer to the removal of condensate formed in steam lines due to the radiant heat loss of the hot steam pipes to surrounding air and are required for the protection of the steam system. (Drip Traps remove the condensate from the steam lines where the process traps remove condensate being generated by the actual process.) Drip traps should be placed 150 to 300 feet apart on straight runs of piping, before elevation changes, and before critical equipment such as Regulators and Control Valves. See description below of typical drip leg configurations.
Condensate must be removed from steam lines to protect piping systems from dangerous water hammer conditions.
Steam moving at high velocity can engulf a slug of condensate and propel it at extremely high speeds down the length of a pipe.
Why Condensate Safety Load Factors and Warm-up Loads need to be considered: During start-up, when the piping system is cold and steam begins to flow thru the pipes, steam is condensing very quickly because of the energy required to heat all the cold surfaces. Furthermore, the steam pressure in the system which is required to push the condensate through the steam trap into the return line, is low before the system comes up to full pressure. Therefore, condensate is being generated at a maximum rate and the steam pressure used to push the condensate out of the system is at a minimum. If the traps are sized for the normal running loads and normal system pressures, then they would be undersized for the start-up condition. In a supervised start-up, condensate drain valves located throughout the system, are manually opened to drain excessive condensate generated by the cold piping system; relying less on the steam traps. Therefore, the steam traps selected for a system with a supervised start-up can be more closely sized for the actual normal running load.
Drip Leg Before Regulator or Control Valve
Drip Leg Design Criteria: • For systems with automatic start-up, L to be 28” minimum (= 1 PSI minimum head pressure) • Drip leg diameter should be equal to steam main diameter (up to 4” in size) Drip Leg in a Steam Main
Drip Legs should be installed directly ahead of regulators and control valves to minimize erosion to valve trim and flooding of valve bodies.
Branch lines should always be taken off the top of the steam main pipe.
Pressure Regulating Valve
Steam Main
Steam Main
Large diameter drip legs ensure that condensate in steam main is properly collected. Length of drip leg gives head pressure to drain the trap after shutdown.
Gate Valve
L
6” Min.
To condensate return
Strainer
TD600L Drip Trap
To condensate return
TD600L Drip Trap
Dirt Pocket for accumulation of pipe scale & debris
Strainer
Drain Valve
Drain Valve
Drain Valve used to discharge debris
Strainer recommended to prevent dirt from entering trap
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