1. #1
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    Eno821302's Avatar
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    Apr 2006

    Question Cold Weather: Dry or Wet?

    Okay- sounds obvious... maybe it's a fly poop / pepper type situation but I'd like to hear some other opinions on it.

    I work in what can be one of the harshest climates in North America- a place that records more sub-zero temperatures than anywhere else in this province. Naturally, this doesn't mean that we never have to go to work... and this climate can require some pretty extensive modifications to normal operations.

    Pretty basic question: In cold weather (-15C and beyond), is it better to run a dry pump or a wet pump?

    The way I see it is wet:

    A pump system full of water is going to take a lot longer to potentially freeze than one that has little pockets of water and moisture built up inside it. On scene, no matter what it is, the pump is recirculated a little faster than normal to keep things nice and warm... We generally run wet back home where I volunteer where climates can be equally daunting.

    A couple of things make the wet pump an attractive alternative:

    1) Pump compartment heaters
    2) Pump heat trays (underbelly trays that shelter the pump manifold)
    3) Short runs


    Admittedly, the other system has merrits as well. You can be pretty sure that no matter how far you have to go, your pump is not going to be one gigantic block of ice (unless your tank to pump valve leaks from dry seals from running a dry pump).The problems I've encountered in the field with dry pumps, however is that often enough the drains are opened up in the hall and generally aren't closed before the next run. On scene, the drains are generally frozen open and while some pressure can be achieved the entire scene becomes a sheet of ice. Some pretty significant ice chips can also clang around inside the pump manifold itself... My issue is that you never really know how "dry" the pump is.

    So besides those things I've listed- any other opinions / reasons for or against either or? I'm not concerned about right or wrong- but I am interested in some outside feedback to help put another tool in the proverbial toolbox.
    Last edited by Eno821302; 12-05-2008 at 09:52 PM.
    Ian "Eno" McLeod
    Senior Firefighter /EMT-A, A Shift
    HESD / OFD
    "To me, the charm of an encyclopedia is that it knows and I needn't."

  2. #2
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    Jan 2007
    Pa Wilds

    Default Cold Weather Ops.


    Here on the top of the Allegheny Front, it is not unusual to see temperatures in the - 20 deg. F range (- 30 C). Our policy is to drain all pumps with particular attention to any drain drops and low routed lines. Some manufacturers are not careful to route lines so that they have drop to the drain point, so it becomes necessary to apply air pressure to pump and piping and blow these lines out. Past experience with American LaFrance beginning in 1917 (passed down from old chief engineers) through L model Macks with globe valve drains, CF's with single point master drains, and finally through Pierce, Sutphen and KME, each engine has its peculiarities with regard to freezing. While I agree that the main pump will probably not freeze making a 3 mile run to the scene, I have experienced freeze-ups of drain lines on a 1 mile return trip where the drain drop was exposed to the wind passing under the engine. Since our policy is to have the pumps dry, we do not need to be concerned with "Taxi Service" engines sitting in the cold and not being pumped. Quints are particularly vulnerable since mutual aid calls here may necessitate a run of 20 to 40 miles and in the end never see the pump charged. These incidents make the damage due to freezing the tank to pump vale a particular problem. Expanding ice pushes the ball away from the seat and results in a permanently leaking tank and a perpetually full pump. A swing out valve and a spare valve repair kit is an essential part of out inventory. I agree that you must close the drains before leaving on the next run. We have a sign for the steering wheel when they are open.

    Hope this helps with your inquiry.

  3. #3
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    Sep 2005
    So of Can. / N. of Mexico

    Default Wet or Dry Pump

    There was a big long thread on this last winter. You might be able to search for it. I think it was about 65 - 70% wet and 30 -35% thought they should be dry. I prefer dry myself.

  4. #4
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    Apr 2006

    Thumbs up

    Thanks to both of you so far. I did a brief forum search and wasn't getting anything pertinent but I'll take another stab at it. If I can find the thread I might just close this one out.

    Very good feedback Kuh... thanks!
    Ian "Eno" McLeod
    Senior Firefighter /EMT-A, A Shift
    HESD / OFD
    "To me, the charm of an encyclopedia is that it knows and I needn't."

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    Nov 2002
    New England


    Its been my experience that most apparatus arent maintained to a level that would allow for a completely dry pump. Valves leak by. Tank fill valves for example are the most likely to leak by because of their frequent use and partially closed operation which damages the ball and or seats. Also, we often encounter repair lists from departments that include "their pump keeps filling with water" only to find that someone left the pump cooler valve open. As most of us know the pump cooler is run to the water tank which will back flow into the pump when the pump is not in use. A simple check valve at the tank would prevent this issue if a dry pump is prefered, yet most manufacturers dont include one.

    I personally think a wet pump is more practical for the above reason and also the increased thermal mass that it provides. For "in service" use this should be sufficent to keep the pump protected. Of course for extended inactive on scene use the pump should be circulating water. The down side of the wet pump as was mentioned is the small drain lines and other extremities of the water system that are not protected by the mass or heat pans. If the apparatus was spec'ed and built with this issue in mind it shouldnt be an issue.

    For out of service puposes I agree a dry pump and tank is best.

  6. #6
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    Funny problem we're having with this situation...

    Even though Pierce has told us to keep the stud pump "wet" and that's an SOP we try to maintain in our environment, the truck's engine cooler draws from the pump manifold itself.

    Funny little problem here:

    When we shut the pump off- the engine cooler drain drains the pump manifold... I accidentally left the tank fill / recirc on the other day and through the course of the shift drained half the tank of water too (drain is located over a grating- so went unnoticed through the next shift).

    Anyone else have this problem?
    Ian "Eno" McLeod
    Senior Firefighter /EMT-A, A Shift
    HESD / OFD
    "To me, the charm of an encyclopedia is that it knows and I needn't."

  7. #7
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    Hernando MS USA


    The best advice I can give is do what makes sense. If your department is more comfortable with the pumps dry then drain them. If it really don't matter then leave them wet. My department has had some really junky equipment over the years and the best option we had at that time was to keep the pumps drained. It has continued until now when our equipment is in much better condition. Old habits die hard I guess
    To err is human, To forgive divine and at times I am as much of both as you will ever find

  8. #8
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    Lots of variables. At my career job we leave them wet and circulate on scene. But we have pump house heaters on all the apparatus and mostly response times that are short enough (with the heaters). It works there, we haven't had a pump freeze yet. However, at my vol. dept we drain them and prime them with RV antifreeze or alcohol. The outlying district engines have no pump house heaters, and sometimes long response times. It works there too.

  9. #9
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    New York

    Default The following is from Waterous service tips web page

    Hope this service bulletin courtesy of Waterous Co. sheds a little more light on this subject... enjoy.


    Extend the Life of Your Pump with
    Tips from the Pros.

    Cold Weather Operations.
    If you are looking at this article, we can only assume you are one of the many individuals who 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.

    The Waterous' recommendation for cold weather operation of Waterous Fire Pumps is simple: “If the pump is exposed to freezing temperatures, drain all water from pump, lines and accessories”. Is it really that simple? Read on……….


    If the fire department elects to run a “dry” pump during cold weather conditions it is necessary to drain the pump completely. To properly drain the main cavity of the fire pump, the tank to pump and tank fill valves need to be closed and the main pump drain opened and remain opened until the water is drained out.

    If the tank to pump and/or tank fill valve(s) are leaking, the pump will not remain drained. Leaving the drain valve open while the apparatus is parked will keep the pump dry, but will also allow the booster tank to drain down, requiring someone to periodically monitor the water level in the booster tank between uses.
    In addition, leaving the drain valve in the open position while it is subjected to freezing conditions may cause it to freeze in the open position, which could render the pump inoperable.


    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”


    1. Minimal chance the pump is going to freeze.

    2. Opportunity to ensure that the tank to pump and tank fill valves are sealing properly.

    3. 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.


    1. 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 is unable to be seen until the fire pump requires disassembly. Other signs of damage may be vibrations and/or metallic sounds coming from the pump, water externally leaking from the main fire pump body and/or body halves, water leaking from components attached to the fire pump or a failed annual pump service test.

    2. 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.

    3. 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. The amount of build up is further compounded by the water quality for the department. Once the fire pump is engaged and water is circulated the excessive build up is broken loose and may create problems with the discharge relief valve system (plugged strainer screen), scoring to the discharge valve seats, damage to the individual discharge valve drains, damage and scoring to the priming valve and other accessories that utilize o-rings and/or seals on mating surfaces. It is important to operate the fire pump periodically to minimize the chances of this condition occurring.

    4. Priming of the fire pump may be required.


    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 (approximately 1/8 to ¼ from closed) open 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.



    1. Priming the fire pump before use may not be necessary.

    2. 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.

    3. There is a reduced chance of dry run conditions on the mechanical seals and/or packing mating surfaces during initial pump start up.


    1. 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.

    2. 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!

    3. 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.

    The following is a sad (but true) story!

    An apparatus with a “wet” pump is kept in a station at seventy (70) degrees Fahrenheit. The apparatus has all of the cold weather accessories (pump house heater, under body pump house enclosure, etc.) on it.

    The apparatus responds to an early morning medical incident one (1) mile away, traveling at an average speed of thirty (30) miles per hour with a temperature of two (2) degrees Fahrenheit. Upon arrival at the incident the apparatus operator forgets to engage the fire pump and the apparatus sits at an idle for fifty-five (55) minutes. After returning to the apparatus the apparatus operator realizes his error and returns the apparatus to the station where it is allowed to thaw out.

    After one hour of (1) hour of thawing in the fire station and a subsequent shift change, the new crew responds to another medical incident meeting the same response distance and elements as the first incident.

    Upon arrival at the incident scene the apparatus operator attempts to engage the fire pump and the apparatus engine stalls. After further examination he finds that the water in the main pump cavity was frozen solid. This condition resulted in the impellers being frozen in position.

    This apparatus was immediately pulled out of service and a NFPA service test performed to determine if there was damage to the fire pump and its accessories.


    We hear comments from both sides on how long water takes to freeze and that a small amount of water will freeze solid faster than a large amount of water does at the same temperature.

    On one hand a small amount of water that has frozen solid will create a small amount of damage. On the other hand a large amount of water that has frozen solid will create a large amount of damage (it just takes a little longer).

    The fact remains that damage can occur throughout the freezing process and is magnified by the amount contained within the pump and its components!

    Another sad but true story!

    What happens to a “wet” pump when the heating system in the fire station fails?

    A department in Minnesota experienced this condition when a two way radio was keyed in a squad car that was leaving the apron of a fire station. The radio frequency caused a north facing apparatus bay door to open. Since the squad car left the facility, the overhead door remained opened for approximately two hours with a temperature of minus twenty (-20) degrees Fahrenheit and a north wind gusting over twenty (20) miles per hour.

    The wind gusts were enough to blow out the pilot lights on the heating system in the apparatus bay. A firefighter happened to stop in the station on his way to work and encountered water flowing from several broken sprinkler pipes and heads in the apparatus bay. There was water flowing from a restroom just off the apparatus bay in which the toilets and their tanks froze and burst, adding to the situation.

    The four fire apparatus within the station experienced the most damage. The fire pumps were frozen solid. It took a propane heater pointed towards the intake fittings on both sides of the apparatus for

    several hours to thaw the fire pumps. The flanges and mounting brackets on virtually every discharge valve were cracked and/or broken off. Several of the discharge valves required complete replacement. All of the priming valves, master drain valves and independent discharge valves on all four apparatus required complete replacement. The discharge and intake relief valves and the pilot valves required complete replacement also. The lone aerial apparatus in the station required a new hydraulic cooler since it was flooded with water at the time the incident occurred. Three of the four apparatus required new impeller shaft assemblies due to the distortion of the impellers and wear rings.


    The individual discharge valve drains (provided by the apparatus builder) on the Waterous discharge valves are located after or down stream from the discharge valve ball and seal. It is recommended that after each use each individual discharge valve drain is opened and remain opened until the water has drained out completely. Individual discharge valve drains will freeze early on since they are down stream of the discharge valve and not exposed to water circulation that occurs within the main fire pump when it is in operation.

    NEVER open a main pump drain or discharge valve drain when under pressure. Damage to the o-rings and/or seals may occur resulting in a leaking drain valve.


    The pump house is defined as the enclosed area surrounding the fire pump and its accessories.

    Pump house heaters are an auxiliary component consisting of a heater core(s) and fan(s). The heaters are usually written into the apparatus specifications and are commonly found on apparatus in cold weather climates.

    The main purpose of the pump house heater is to provide limited freeze protection to the gauges, gauge lines and other small components that are located in the upper area of the pump house (the area above the fire pump). Pump house heaters do little to protect the fire pump or components that are located beneath the fire pump.


    Under body pump house enclosures (belly pans, heat shields, etc.) are made of metal. The purpose of the enclosure is to close off the underside of the fire pump and pump house. For the enclosure to be effective, the apparatus exhaust system (usually the muffler) runs through the enclosure.

    When properly installed, the enclosure traps heat from the apparatus exhaust system in the pump house, providing increased protection to the fire pump and its accessories when exposed to freezing conditions.

    Since heat rises, the lower and upper areas of the pump house see protection. The harder the apparatus engine is working, the more heat is generated.


    Measures should be taken to ensure that slippery conditions that result from water that is discharged around the apparatus and around the incident scene be treated with sand and/or salt for better footing.
    When performing drafting operations the access routes to and from the incident scene to the fill site should also be treated with sand and/or salt for safer driving conditions.

    We hope this information helps, if you need additional information feel free to reply by email (sales&service@waterousco.com) or call us at (651) 450-5200.

  10. #10
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    Jan 2009


    Awesome info... thanks again for the feedback.
    Ian "Eno" McLeod

  11. #11
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    Rescue101's Avatar
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    Jun 2001
    Bridgton,Me USA


    Eno,See above thread.We're currently discuccing this,you musta missed it. T.C.

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