Fire apparatus pumping: static water sources
Drafting from static water supplies is a different animal than pulling water from a municipal source; here’s how to get the most from your rig
After what was a brutal winter for much of the United States, warmer weather is finally upon us. And with that warmer weather comes the need to obtain an adequate water supply from a static source.
Sure, drafting from available lakes, ponds and streams are a critical component of rural water supply all year long, but hotter and drier weather brings a greater frequency of outdoor fires. Those fires typically involve vegetation, and, just as typically, they occur in areas remote from a municipal water supply.
Now is a good time to review your department’s equipment capabilities and refresh the skills of your personnel in obtaining needed water from static sources. Many times the ability to get a good draft and maintain it for the entire fire suppression operation has been compromised by a deficiency in one or both of these areas.
For many departments winter weather means frequently draining the apparatus pump and water lines to prevent freezing. So begin your warm-weather apparatus check by ensuring that all of those drain valves on the pump have been properly closed.
Primed and ready
It is critical in drafting operations for the primer pump to be able to exhaust all of the air from the centrifugal pump. Remember, it is the evacuation of all air from the centrifugal pump and discharge lines that creates a negative pressure within the pump causing atmospheric pressure to push water from the static source up the hard suction hose into the apparatus pump.
Give close inspection of the unit’s hard suction hose according to the specifications contained in NFPA 1962. This includes the suction hose vacuum test outlined in A.4.10 of the standard to ensure that the lining of the hose is not drawn into the waterway under negative pressure.
Ensure the apparatus has the necessary tools and appliances for drafting operations. These include, but are not limited to, these four items.
- Intake strainers for the hard suction hose.
- Short lengths of rope for securing hard suction hose.
- Support braces and chafing material to support and protect hard suction hose from vibration during pumping operations.
- Rubber mallet for creating tight coupling connections between lengths of hard suction hose and the pump intake.
Chapter 16 of NFPA 1901 contains the applicable standard for primer pump testing (16.13.5). With the apparatus pump dry, exercise the primer pump to ensure that it operates properly. Once the primer pump is engaged, the operator should observe primer pump lubricant being discharged underneath the apparatus followed by a steady stream of water and lubricant.
The pump should be primed within 30 seconds of the primer pump being engaged for pumps rated at 1,250 gpm or less or 45 seconds for pumps rated at 1,500 gpm or more. After properly exercising the primer pump, refill its lubricant to the proper level.
Science of drafting
Now that you know that you have all the requisite equipment for drafting, and that your pump priming operation works properly, here are some useful tips for better drafting operations from static water sources.
Remember that the height of the lift — from the surface of the water to the intake of the pump — is the critical factor in drafting operations using a centrifugal pump.
Apparatus pumps rated at less than 2,000 gpm must be able to achieve a draft from a lift of at least 10 feet; the lift height drops to 6 feet for pumps rated at greater than 2,000 gpm. While apparatus can and will achieve a draft from a height greater than 10 feet, the pump’s rated output starts to diminish and the risk of cavitation and vacuum leaks increases.
Suction hose friction loss is another factor in reduced pump capacity. As you add extra lengths to the suction hose assembly for deep lifts or for hard-to-reach water sources, friction loss increases, which also reduces pump performance.
Know your elevation. Due to lower atmospheric pressure, pump lift capability and gallon-per-minute performance naturally reduce as geographic elevation increases.
Locate the source
Tour your response district and identify available static water sources in advance of needing them. In the Chesterfield County (Va.) Fire and EMS Department where I served, those at one of our stations with a large response area with no municipal water supply took a very innovative approach to this recon.
They made arrangements with the regional law enforcement aviation unit to go up and photograph all the potential static water sources in their district. After the photographs were taken, the potential sites were evenly distributed among the three shifts for follow-up site visits during which they obtained the following information:
- Was the site a viable water supply for fire department drafting operations?
- Was vehicle access to the site on public or private land? If it was on private land, would the land owner allow the fire department access?
- If the site was accessible to fire apparatus, was it available year-round?
In cases where the site was located on private land, and the land owner was agreeable to allowing departmental access, a written agreement to that affect was executed between the owner and the fire department.
Each of the identified viable drafting sites was then given a unique numerical identifier. Those site locations were entered into the county’s computer-aided dispatch system and entered on the map cards carried aboard the station’s apparatus. In addition, aluminum signs were posted on the roadway to identify the site’s location; this was particularly useful for those sites that were not easily viewed from the hard-surface road.
Preparation and planning for your next use of a static water supply and how it gets accomplished can be a critical factor in the outcome of your next fire. How prepared is your department?