Most fire companies are seeking information on whether they should run a “dry’ or a “wet” pump during cold weather operations.
This article covers the Waterous recommendation along with several other “pros” and “cons” related to running the pump “dry” or “wet” in cold weather environments.
WET PUMP OPERATIONS:
Since moving water doesn’t freeze, the fire pump should be engaged and water circulated during cold weather conditions. If circulating water through the apparatus booster tank, the tank to pump valve should be fully open and the tank fill valve partially open (approximately 1/8 to 1/4 from closed) to allow adequate circulation. The apparatus operator should continually monitor the pump temperature by feeling the intake fitting with their bare hand to ensure the pump isn’t overheating. If the pump is equipped with the Waterous “Overheat Protection Manager” (OPM) the apparatus operator should monitor the OPM warning light on the pump operator’s panel. If the warning light is illuminated the water temperature within the fire pump and apparatus booster tank is overheating and the pump must be disengaged or fresh water must be introduced into the pump through an intake to avoid severe damage to the fire pump and its components.
If operating from an outside water source, the apparatus operator should ensure that some water is being circulated through a discharge or tank fill valve to minimize chances of the pump overheating..
Wet Pump PROS and CONS
PROS:
- Priming the fire pump before use may not be necessary.
- The mechanical seals or packing remain in water keeping them pliable and minimize the chances of calcium build up since they are not subjected to atmospheric conditions.
- There is a reduced chance of dry run conditions on the mechanical seals and/or packing mating surfaces during initial pump start up.It is strongly recommended to exercise the system 10 to 20 minutes a month even when not regularly used.
CONS:
- The chances of damage to the fire pump and its components increase if the pump is not engaged and water isn’t properly circulated when exposed to freezing conditions.
- The chances of damage to the fire pump and its components increase if the pump is not engaged and water isn’t properly circulated when exposed to freezing conditions.
- The chances of the fire pump and its components freezing increases with excessive response distances and increased road speeds. Not to forget that the colder it is, the faster things will freeze!
- The potential for repair costs increases when running a “wet” pump due to the potential for damage to the fire pump and its accessories as a result of freeze up.
DRY PUMP OPERATIONS:
A “dry pump” is not necessarily dry. Discharge and intake (compound) gauges, gauge lines, individual drain lines, pressure lines and other components with small orifices will have a tendency to retain water. Unless they are disconnected and allowed to drain they may retain water, resulting in freezing and subsequent damage to the components. Since disconnecting and draining of the lines is labor intensive, this practice is seldom if ever done. This promotes the need for pump house heaters and under body pump house enclosures when operating in climates where freezing conditions are a concern.
Dry Pump PROS and CONS
PROS:
- Minimal chance the pump is going to freeze.Minimal chance the pump is going to freeze.
- Opportunity to ensure that the tank to pump and tank fill valves are sealing properly.
- Ideal for situations where extended response distances to and from the incident and/or increased speeds (highways, freeways, etc.) are obtained. With no water in the main cavity of the fire pump and its accessories little, if any, damage will occur.
CONS:
- Requires periodic opening of the main pump drain to ensure the main pump cavity isn’t partially full of water. A partially full pump will freeze rapidly and will initially cause damage to the impeller shrouds and vanes. This damage may be unable to be detected until the fire pump requires disassembly. Requires periodic opening of the main pump drain to ensure the main pump cavity isn’t partially full of water. A partially full pump will freeze rapidly and will initially cause damage to the impeller shrouds and vanes. This damage may be unable to be detected until the fire pump requires disassembly.
- If the main pump drain is left open and the tank to pump and/or tank fill valve(s) are leaking, the apparatus booster tank may be low or empty. This condition requires constant monitoring and filling of the booster tank. Also, an open drain can freeze in the open position.
- If the pump is left “dry” for extended durations without the fire pump being operated, an excessive build up of calcium and/or rust deposits will accumulate inside the main fire pump cavity, and may create problems with the discharge relief valve system. It is important to operate the fire pump periodically to minimize the chances of this condition occurring.
- Priming of the fire pump may be required.
