What happens when a steam trap fails in the open position?
- Condensate backs up and floods the heating equipment
- The boiler water level rises above normal
- Live steam blows through into the return line
- The steam main fills with trapped air
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C. Live steam blows through into the return line
A trap stuck open passes steam straight to the returns, wasting fuel and overheating and pressurizing the condensate system. Flooding of the equipment is what happens when a trap fails closed.
Reference: Steam systems: trap failures
On what principle does an inverted bucket steam trap operate?
- A bellows filled with volatile liquid expands when steam heats it
- Steam under the bucket makes it float and close the valve
- A disc is held shut by the speed of flashing steam
- A bimetal strip bends as the condensate cools down
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B. Steam under the bucket makes it float and close the valve
The trap works on the density difference between steam and water: steam entering under the open-bottomed bucket makes it buoyant and it rises to close the valve; when condensate fills it, the bucket sinks and the valve opens. The expanding bellows describes a thermostatic trap.
Reference: Steam traps: inverted bucket type
Why should an inverted bucket trap be primed with water before it is put in service?
- Without water in the body the bellows will overheat and rupture
- Water in the body is needed to dissolve the air ahead of the steam
- Without a water seal the bucket cannot float, and steam blows through
- Water in the body keeps the trap from freezing during a shutdown
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C. Without a water seal the bucket cannot float, and steam blows through
The bucket needs water around it to become buoyant when steam enters. With a dry body the bucket hangs down, the valve stays open and steam passes continuously. An inverted bucket trap has no bellows.
Reference: Steam traps: inverted bucket type