Getting the Most From Large-Diameter Hose
Large-diameter hose has been one of the most significant tools for increasing the water supply capability of the rural fire service. Moving large volumes of water (750 gpm and up) over several thousand feet is now commonplace in rural areas not serviced by pressurized water sources and hydrants. Rural fire departments were the first to use large-diameter hose on a widespread basis. As the advantages of this water supply system became apparent, the use of large-diameter hose began making inroads into suburban and urban fire departments.
An accessory that is commonplace in rural water supply operations but much less common in suburban and urban communities is the inline relay valve. This device can help you use your large-diameter hose to its fullest potential in almost any setting, whether rural or suburban.
The inline relay valve allows boosting the pressure on a large-diameter hose line by connecting a pumper without shutting the original line down. The valve has a straight-through waterway, a gated discharge and clappered auxiliary inlet.
Before hooking up the pressure boosting pumper, the water flows straight through the valve with the gated discharge closed and the auxiliary inlet closed off by the clapper. The pumper can then hook up by running a hose from the gated discharge of the inline relay valve to the suction side of its pump and a hose line from the pressure side of the pump to the auxiliary inlet of the inline relay valve. As the gated discharge of the inline relay valve is opened and the pump begins boosting the pressure, the clapper swings and allows water to flow into the auxiliary inlet. The pumper can continue to raise its pressure until a discharge pressure of typically 150 psi is reached or until the residual incoming pressure drops to less than 10 psi.
The key to successful use of inline relay valves is having short lengths of large-diameter hose available. Short lengths limit the amount of friction loss by limiting the length of hose the water has to travel through, cuts down on confusion and spaghetti in the street, and makes it much easier and quicker to hook up to the valve with limited manpower. Standard 100foot lengths certainly will work, but short lengths make the job a great deal easier and provide for more efficient water flow. It is suggested that three short lengths be supplied with each inline relay valve, a 10-footer, a 25-footer and a 50-footer.
In the rural setting, long hose relays are quite common, resulting in frequent use of inline relay valves. These valves are installed in large-diameter hose lays every 1000 to 1500 feet as the hose is first put in the street. The hose line is then charged and a minimal water supply established with a pumper at the water source and an attack pumper at the fire scene. As additional manpower and pumpers or mutualaid companies become available, they can be assigned to relay valves to boost pressure. If these companies are equipped with at least two short lengths of largediameter hose, a 25-footer and a 50-footer, hooking up with a minimum of manpower is a simple matter. If opposite sides of the truck are used for suction and discharge, the 25-foot length can be used for the port closest to the relay valve and the 50-footer can be used for the port on the other side of the truck. This provides for the maximum utilization of both lengths.
The operating principles of the inline relay valve are similar to the Humat valve and other hydrant valves intended to allow charging a supply line and having the flexibility of supplementing the water supply without shutting the line down. As a result, communities that have both rural and hydrant water supply districts can take advantage of the inline relay valve to improve their water supply capability.
The use of a 10-foot length of largediameter hose is particularly useful for this evolution. The short length is attached between a hydrant outlet (steamer fitting preferably) and the inline relay valve. The hose lay can be either a forward or reverse lay connected to the inline relay valve, depending on local standard operating procedures. This evolution is more advantageous when used with forward hose lays.
This arrangement has a great deal of flexibility in addition to maximizing potential water flow with the large-diameter hose. One procedure could have an initial attack pumper go directly to the scene of a fire and go to work. A water supply pumper can lay out the 10-foot short length, inline relay valve and hose lay to feed the initial attack pumper establishing a very quick but minimal water supply. The water supply pumper can then go back to the hydrant with limited manpower, just a pump operator if necessary, and use the 25-foot and 50-foot short lengths to hook up to the inline relay valve and increase the water supply to the fire scene.
Connecting an additional hose line from a gated outlet of the hydrant to the gated suction of the pumper will help to increase the residual pressure to the pumper. It is important to make sure that all gate valves are fully open. The large-diameter gate valves are not of the indicating type and it is critical that they be all the way open to allow for maximum water flow.
Another evolution that can be quite effective with the inline relay valve is for a pumper to lay out a 10-foot short length, its inline relay valve and the hose lay. The truck can stay at the fire and inline pump. As additional manpower and pumpers or mutual-aid companies arrive, the water supply can be increased by hooking up to the inline relay valve without shutting the line down.
An example of the hydraulics involved is given by the following. A hydrant on a large water main has a residual pressure of 50 psi when flowing 750 gpm. A 600-foot hose lay is stretched by the first-due pumper and it goes to work at the scene. With 4-inch hose and 10-psi friction loss per 100 feet, the 60 psi at 75 gpm available at the hydrant will just about flow 750 gpm through the 600 feet of hose. A 1000-gpm rated mutual-aid company arrives and hooks up to the inline relay valve. The discharge pressure is increased to 150 psi, while the residual drops to 30 psi. The flow is increased to 1200 gpm.
The use of large-diameter hose was at one time the domain of the rural fire service. As suburban fire departments became aware of the advantages of largediameter hose they began using it, but more as a replacement for multiple lines of 2½-inch hose. Therefore, this device has not been in widespread use in suburban operations. The suburban department that has both rural and hydrant water supply districts should take advantage of the flexibility of the inline relay valve to get the most out of large-diameter hose.
Dave Demers is a lieutenant and training officer with the fire department in Lunenburg, Mass. Formerly manager of the Fire Investigations Department at NFPA, he is now president of the fire protection consulting firm of Demers Associates, Inc. Dave has been involved in fire fighting activities for the last 15 years.