By James Flanagan
The Plymouth (WI) Fire Department, like many departments with a rural fire exposure, found the need to improve its rural fire protection class rating. Currently, its rural rating is a PC-8B. The goal was to achieve at least a PC-6 to provide relief to businesses and homeowners on the cost of their fire insurance premiums.
You are viewing: A Jet Siphon Is Used For Which Application
Like many departments with volunteer members, a committee was formed whose makeup could tap the members’ varied backgrounds from engineering to IT specialists, all of whom proved beneficial in the project.
The committee’s firefighters began with training sessions presenting various fire flow formulas and general background knowledge of friction loss and the factors affecting fire flows through hoses and appliances.
A PowerPoint® program on the basics of the ISO rating system was developed and presented to the committee and later to the entire department. The presentation focused on many criteria used in gauging a department’s adherence to the elements that compose the fire service’s 50% portion in the ISO PPC rating schedule. Also presented were the components for dispatching (10%) and water supply system (40%) in the municipal sector.
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The committee’s approach to the project was to develop data that would benefit not only the Plymouth Fire Department but also many others within the county. To develop valid and repeatable data, some additional testing tools were needed and developed to provide the means to test and validate some of the committee’s hypotheses. A water depth test gauge was developed to convert the increase or decrease of water levels in our portable drop tanks to gallons.
The committee set about confirming that the department’s drop tank’s depth could be converted from depth in inches to gallons. Initially, this was done by taking a container that, when filled to the appropriate level, contained 50 gallons. Then, 50 gallons at a time, the drop tank was filled to a level of 500 and 1,000 gallons, with each depth noted and marked in the tank’s inside surfaces.
These measurements were converted to cubic feet and then multiplied by 7.47 gallons per cubic foot. The department’s drop tank measures 12 feet 8 inches × 12 feet 8 inches × 30 inches high, which converts to 100 gallons per inch of water depth.
The interior surface of the drop tank is now marked and labeled with 500-gallon increment levels.
The initial objective was to analyze the consumption requirements of our current jet siphon system. The Plymouth Fire Department uses a manufactured unit that is placed into the female end of a 6-inch draft hose 12 feet long, which directs a stream of water into the center portion of the hose that discharges through a 7⁄8-inch orifice supported by a 1¾-inch handline. This system generates a venturi-like effect that draws additional water by means of the partial vacuum it creates in the immediate area of the discharged stream.
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Initially, a problem arose when we placed the system on the ground outside of the drop tank. A portion of the stream backflowed from the draft hose. The leakage was significant enough that the loss had to be accounted for if we were to obtain an accurate flow rate. The team found that by placing the pickup end into the top of a 5-gallon pail, the water was captured to a point that it remained level and did not overflow the pail.
At this point, we were able to run our flows and be assured that the discharged amount of water could be measured with no loss to be accounted for. Depending on a department’s system design, some type of capture vessel may be required if you run a similar testing evolution.
Having determined that we could measure the amount of water flowed by measuring the change in the depth of the water in the tank, we made a simple depth gauge from 2-inch (inside diameter) clear PVC plastic pipe 60 inches long, or twice the height of the drop tank; a 2-inch end cap; a reducing fitting (2 inches to 1½ inches); a couple of 2-inch-diameter fish bobbers; and a dowel.
We glued the reducing fitting to the bottom end and drilled it with six small ¼-inch holes to allow the water to enter into the column. The end cap for the top should have a small hole, less than 1⁄8 inch, drilled in it. We found that too large a hole would not dampen the bobber’s movement in response to small wave actions on the surface. We found that the glue seam of the two halves of the bobber was not perfectly aligned, so we had to carefully sand the overlaps flush to allow it to fit within the tube and still retain a distinct color line. We removed the bobbers’ fishing line attachment systems. This provided a recessed opening on the button end. An appropriately sized dowel can be inserted or glued into the bobbers, with one bobber placed on each end of the dowel. The dowel’s length should be such that when the tank is empty, the red/white seam rests at the same height as the top of the tank frame.
The red/white seam at the top of the bobber will be used to mark the start and stop points. To mark these points, blue painter’s tape was applied to the outer surface of the tube, and the marks were easily read when the measurements were recorded. We found it necessary to begin with the tank filled to about the 500-gallon level. Also, remove any ripples at the tank’s bottom so it is sitting flat to ensure that its shape is constant.
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