DRY HYDRANTS REVISITED

BY MICHAEL HANLEY

Fire districts that do not have a public water supply must rely on alternate water sources for fire protection. New fire pumpers must include a minimum of 1,000 gallons of water and tanker trucks 3,000 gallons of water. These minimum specifications are supplemented with as many dry hydrants as possible.

A dry hydrant is a pipe (minimum six inches) connected to a static water source such as a pond or a tank on one end. The other end is a fire department connection configured for quick and easy access by fire apparatus.¹

(1) Standard hydrant and curb valve: hand pump, valve wrench, curb valve (right of hydrant). Note the 41/2- to six-inch adapter permanently mounted on the hydrant. (Photos by author.)

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In Connecticut, freezing is a real problem that must be considered when designing a dry hydrant. When water freezes in a pipe, one of two possible consequences may result. The first outcome may be that the frozen water will crack the pipe. Depending on the crack and the type of soil surrounding the pipe, an air leak may result. The air leak will delay or even prevent a successful draft. If the pipe does not crack, the ice will act as a plug, preventing a successful draft.

To protect against freezing, we must ensure that the supply pipe and strainer are buried deeply enough—in Connecticut, four feet below the surface is sufficient. When the water level in a pond or stream is within the four-foot depth, the water must be prevented from entering the riser pipe when not in use. Installing a valve will prevent the water from entering the riser until it is needed. Opening the valve allows the water to enter the riser pipe up to the level of the water source (pond or stream). After closing the valve, the water left in the riser can be removed by using drains or pumps.

The Bethany (CT) Fire Department has investigated various dry hydrant designs for a water level that is within the freeze line.

STANDARD HYDRANTS

Using a standard hydrant as a dry hydrant to keep the water below four feet when not in use is one alternative.

Positives

This type of hydrant comes with a built-in shutoff. When the hydrant is closed, water left in the riser drains out by way of drain holes.

Standard hydrants are easy to install, and replacement parts are readily available.

• Standard hydrants are expensive, compared with dry hydrants.
• The flow rate is much less than that of a six-inch dry hydrant. The maximum flow water we were able to achieve from a standard hydrant was 1,100 gallons per minute be-cause of the high friction loss caused by the internal design and components. Losses in a pressurized system are minimal but will restrict water flow significantly when drafting. The 41/2-inch steamer connection further reduces the flow rate. This compares to 1,400 gallons per minute using a dry hydrant in a similar layout, an increase of 300 gallons per minute.
• A 41/2- to six-inch adapter will be needed to complete the connection, adding to setup time. The Bethany Fire Department mounts these adapters directly on the hydrant to reduce setup time.
• As standard hydrants age, air leaks develop in a number of places such as where gaskets (21/2-inch connections) and sealers are used. Lack of air tightness further reduces the flow rate and increases the time to establish a draft. Severe leaks will also prevent the ability to draft at all.

Negatives

In areas with a high water table, the drain holes must be plugged in the hydrant to prevent water from entering the barrel. The remaining water in the barrel must then be pumped out using a small manual or electric pump after the hydrant is closed.

Standard hydrants may also be used when they are located below the water source creating a pressure at the hydrant. In Bethany, we have one such design, which is supplied by a reservoir. The elevation creates between 20 to 30 pounds per square inch (psi) of pressure at the hydrant and delivers about 800 gallons per minute. The pressure varies because of fluctuation of the reservoir water level. The reservoir lies about 100 feet above the hydrant. Mul-tiply this by 0.434 (in-crease in psi for every foot in elevation), and subtract the friction loss (six-inch ductile pipe). The result comes very close to the observed pound per square inch.

If a standard hydrant must be used, we recommend that only new hydrants be installed. Used hydrants, even when donated, should be a cause for concern. You must ask the following questions before accepting a used hydrant:

• How old is it?
• Are replacement parts available?
• Has it been tested for air leaks?
• Why isn’t it used anymore?

(2) The old setup—standard hydrant with a maximum flow rate of 1,000 gpm.

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A used hydrant may cost you more money than a new one in the long run. Digging up a bad hydrant is bad public relations, and that is money that could have gone for another dry hydrant. Remember that even a small air leak will increase priming duration and decrease the flow rate.

CURB VALVES

The use of curb valves in conjunction with dry or standard hydrants is another alternative. In combination with a dry hydrant, the valve must be in the open position to allow water to flow to the hydrant. When you are finished using the hydrant, you must close the curb valve to prevent water from rising through the pipe. Use a small hand or electrical pump to remove the water from the riser after the valve is closed. In combination with a standard hydrant, the curb valve may remain opened; the water is turned off using the hydrant’s valve.

• Using the curb valve with a standard hydrant allows replacing or repairing of the hydrant without draining the pond.
• Curb valves are less expensive to purchase and install than standard hydrants.

• Requires special wrenches and pumps.
• There is no easy way to observe whether the valve is opened or closed.

DRY HYDRANTS AND POST-INDICATING VALVES

(3) Installation—supply pipe and post-indicating valve are prepared, placed in the ditch, and secured into the concrete galley.

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Another way of confronting the high water level is to use a six- or eight-inch post-indicating valve (PIV) with a dry hydrant.

• The PIV shows the pump operator at a glance whether the valve is opened or closed.
• The PIV may be opened or closed with the included wrench or a standard hydrant wrench.
• PIVs may be adapted to the size of the supply pipe needed to achieve the desired gallons per minute.
• All the parts used in this configuration are standard. There are no specially designed parts, which facilitates making repairs.

• The initial installation costs much more than that for standard hydrants.
• To prevent ice from forming in the riser pipe, the operator must remember to close the PIV.
• The operator must pump out the excess water in the riser pipe.

Negatives

PLANNING A DRY HYDRANT WITH A POST-INDICATING VALVE

Installing a dry hydrant and post-indicating valve to replace a standard hydrant proved challenging. The old hydrant was failing, and replacement parts were not available. We could not dig out the old hydrant without blocking the water in the supply pipe. Doing so would cause the pond to grain uncontrollably, which would create unwanted silting down the hill and an unfavorable work area.

First, we developed a plan in which we would attempt to block the supply pipe at its source. Then, we would proceed to remove the old hydrant and install a new dry hydrant/PIV combination. A backup plan was devised in case this failed. The backup plan was to drain the pond, a time-consuming process that would add to the cost of the project.

Once our plans were complete, we prepared an Inland-Wetlands permit detailing our intentions and the reasons. The Inland-Wetlands officer reviewed our plans, surveyed the pond, and gave us the go-ahead.

During the planning stage for dry hydrants, we developed a computer spreadsheet (see Figure 1 below) that accepts fixed and variable data about the proposed dry hydrant site. Fixed information includes the following:

• Height above sea level.
• Static lift.
• Average temperature.
• Fire apparatus pumping capacities.

Variable information includes the following:

• Pipe size.
• Type of pipe (PVC, ductile iron, steel).
• Number and types of elbows.
• Length of pipe, horizontal and vertical.
• Strainers.
• Whether a dry or standard hydrant is used.
• The desired gallons per minute.

The variable information may be changed, and the results are instantaneously displayed. For instance, if the desired gpm is not acceptable, then increasing the pipe diameter or changing the elbows from 90° to 45° would help. Helpful hints are displayed, assisting in the design process. For example, if the static lift is greater than four feet and the standard hydrant is selected, the message would indicate that the standard hydrant may not be needed. Of course, if you decided to go with the PIV, there would be no use for standard hydrants. Also displayed for the current static lift are the capacity in gallons per minute and the capacity in percent for each pumper on the spreadsheet.

To test the accuracy of the spreadsheet, we chose existing dry hydrants. The information about the dry hydrant was entered into the spreadsheet. The spreadsheet results ran about 50 to 100 gallons per minute higher than the real-world results. Knowing this, we could predict how a proposed dry hydrant would perform.

INSTALLING A DRY HYDRANT WITH A PIV

On the morning of the project, we attempted to block the supply pipe at the concrete galley. At the same time, we started to drain the pond using a 1,500-gpm pumper. Attempts to block the pipe failed. After a few hours, the pond drained to the point that digging out the old hydrant could begin.

(4) The completed system (left to right)—concrete galley, post-indicating valve, dry hydrant, and access lot with boulder.

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(5) Flowing water—the 1,500-gpm pumper is flowing 1,200-gpm through a two-inch deck gun nozzle. The suction hose is resting on a boulder that facilitated the connection.

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After the old hydrant and piping were removed, the ditch was prepared, and an area around the existing cement galley was cleared. New pipe along with a PIV and riser were installed. Next, the ditch and galley were carefully back-filled. The galley was surrounded with stones; the ditch was filled in with clean fill.

We opted for two 90° elbows instead of two 45° elbows. This decision was based on two factors: the materials and installation cost vs. increase in gallons per minute and the location of the PIV. The horizontal length of the supply pipe is only 20 feet. Only a marginal gpm gain would result with the 45° elbows. If we decided to go with the 45° elbows, that would place the PIV near the edge of the pond. We preferred a more stable ground all the way around the PIV for firefighter safety.

The PIV and dry hydrant were assembled, and the final grading was completed. A coat of paint was applied to all exposed metal, and the area was seeded. The dry hydrant was tested a short time later. A pumper was able to secure a connection, prime the pump, and discharge water through a deck gun within minutes.

The Bethany Fire Department believes it has come up with an improved solution. The dry hydrant/PIV design replaced the standard hydrant arrangement on one of our ponds. At this location, the most we could achieve using the old design was a maximum flow rate of 1,000 gallons per minute. During the late spring and early summer, the flow rate is reduced because of aquatic animals (pollywogs, small fish, and so on) clogging the strainer. This, of course, is the price you pay for using ponds. The new design realized a maximum of 1,300 gallons per minute. An access pull-off allows the fire apparatus to leave the road, providing a safer environment for the pump operator and passing motorists. A large flat boulder was placed in front of the hydrant to protect the hydrant and act as a platform to assist in the connection process.

Our dry hydrant is a six-inch female connection and plug; National Standard Threads are used. The dry hydrant strainer was removed to improve the flow rate. We determined that a strainer at the source and on the fire apparatus’ six-inch intake is sufficient because adapters increase setup times and the chance for an air leak. We have just one type of suction hose; it has a female and male end. The female end attaches to the pumper while the male end connects to the dry hydrant.

Using a six-or eight-inch PIV with a dry hydrant offers many advantages:

• Opening and closing the valve are achieved using standard hydrant wrenches.
• The pump operator is able to tell at a glance whether the valve is opened or closed.
• Using standard materials facilitates repair and maintenance.
• Using the combination of a dry hydrant and PIV provide a great-er flow rate than using standard hydrants and curb valves.
• This setup provides fewer moving parts, seals, and gaskets. It increases reliability, re-ducing maintenance and downtime, therefore establishing a sound draft in the shortest time.

Bethany now has 11 dry hydrants; six more are planned within the next three years. Each dry hydrant is tested twice a year. The following information is logged:

• Hydrant location and number.
• Testing date.
• The pumper performing the test.
• Gallons per minute achieved.
• Priming time.

This information may be demonstrated graphically. The graphs show any negative trends such as increased priming times and decreased gallons per minute. Also, if closely monitored, the graphs may indicate that a fire apparatus pump requires servicing.

When correctly designed and installed, dry hydrants provide reliable and accessible water sources for fire suppression. They facilitate water transportation to where it is needed the most, the fire.²

References

1. See “Dry Hydrants and Static Water Supplies,” Fire Engineering, Feb. 2000.

2. Davis, Larry. Rural Fire Fighting Operation, Book Two—Water Supplies & Water Delivery Techniques. Inter-national Society of Fire Service Instructors.

MICHAEL HANLEY, who has been a firefighter for more than 25 years and is a Connecticut-certified fire department pump operator, is the fire department water source commissioner for the Town of Bethany, Connecticut. He has written the water source specifications for the Bethany Fire Department, reviews proposed residential and commercial subdivisions, and makes recommendations to the Planning and Zoning Commission and the Inland Wetlands Commission. He works with the Zoning Enforcement Office and the Fire Marshal’s Office to ensure that all public safety requirements are met.