Fire Hydrants and Valves
The history of fire hydrants goes back as far as societies’ need to put out fires. Originally, cisterns were needed to hold large amounts of water in the event of emergencies. This water would be rushed to fires by any means from buckets, carts, pumps and pipes.
By the 18th century, water infrastructure allowed fire departments to tap directly into the water supply by means of cutting a hole into the watermain and access water through a standpipe. After the crisis had been passed, the pipe would be plugged and repaired for regular service.
Later developments encouraged the installation of a standpipes that gave firemen easier access water from above ground. They would then be able to pump the water into trucks for additional speed and mobility. These ports would be plugged at the top and be enclosed with a wooded case.
By 1801, the first conception of the fire hydrant was patented in Philadelphia by a city engineer named Frederick Graf. This hydrant was of a wet barrel type including a faucet port on the side and a valve on top.
Improvements were made and by 1958, our first modern hydrant was introduced. Resembling much of today’s hydrants, cast iron was used for the main body with a flip lid to have above ground access operation.
Most of the early hydrants designed were wet barrel style, meaning water sat above ground inside of the hydrant. They use a pressurized system that forces water out for access. The problem with wet barrel hydrants is freezing conditions. Despite this, the wet barrel type is still used in warmer climates where freezing is not an issue.
Developments to the wet barrel style helped to create the dry barrel. These hydrants have similar components however a main valve installed near the bottom allows the barrel to shut off the water to keep the barrel from freezing. The dry barrel also uses a drain valve at the bottom of the hydrant to drain any excess water from the hydrant buried underground.
The design of the hydrant utilizes a stem nut, or operating nut at the top of the hydrant. This access controls the stem that opens the main valve at the bottom of the hydrant allowing water to be drawn up through the barrel.
Various models of hydrants for are made for specific application, implementing different pumper nozzles as well as hose nozzles for smaller applications. Nozzles are made of brass that are threaded in the body of the cast iron top. Pumper nozzles are usually 4” or 4/1-2” while the two hose nozzles are commonly 2-1/2”. Nozzles can be replaced in field.
The most current hose connection is the Storz connection which is designed as a quick coupling for fire hoses. This is a time saver for fire departments that is crucial for fighting fires. Another benefit of this connection is that departments that are helping other cities or towns can quickly hook up to the hydrant without having to worry about the threading of older conventional pipe connections. The connector can be ordered attached to the hydrant direct from the factory or can be field installed. Various threads are available, national standard thread (NST) and national pipe thread (NPT) to name a few.
In the 1930’s, the first design of “traffic” models was introduced to reduce extensive damage if the fire hydrant was hit by a vehicle. This stopped the hydrant from breaking off and creating a geyser of water.
Upon vehicular impact, two lower safety flange rings fracture and stem couple separates below the break line. This allows the above ground hydrant assembly to separate cleanly from standpipe and keeps accidental opening of hydrant. Repair is easily accomplished with economical field repair kit.
Today’s modern hydrant utilize a cast iron or ductile iron inlet shoe to connect to the watermain pipe usually made from ductile iron pipe or C900 PVC Pipe. Inlets can be provided with mechanical shoe, flanged, spin-in or push-on. The most common inlet size is 6.
Barrel standpipe is made of ductile iron with stainless steel stem and brass main valve seat. By removing the top bonnet, internal parts can be replaced in field. There must be an isolation valve installed before the hydrant in order to shut off the water for maintenance.
Barrels are made in various lengths for various climates. Barrels are furnished with a bury line indicator to ensure proper protection from traffic impact. A hydrant extension is available for hydrants that needed to be extended after the final grade is determined.
The main valve is made of SBR rubber and is seated in the main valve shoe made of brass or bronze.
Main valve sizes are generally 4-1/2” or 5-1/4”.
Fire Hydrant Types
Most fire hydrants fit within two categories, wet and dry barrel.
As the name implies, dry barrel hydrants are free of water until its valve is opened. These hydrants are designed prevent issues caused by freezing water inside of the barrel. The dry barrel hydrant is overwhelmingly the most popular style utilized in the united states.
Wet barrel hydrants are very similar to dry barrels except for the fact that they house water inside of the hydrant when not in use. This type of hydrant is perfectly acceptable in regions where freezing water is not a concern.
Located on the top of the hydrant, the bonnet is the rounded cap that surrounds the operating stem nut. The bonnet holds the nut in place and serves to protect the top of the hydrant from collisions or water damage.
The branch pipe connects the cities water main to the hydrant assembly. Extending underground, the branch pipe leads to the site of the hydrant. This size of this pipe is consequently one of the main factors in determining the water capacity of the hydrant. Older systems often used 4” branch pipe however today a minimum of 6” is used to reduce pressure loss and allow for more flow.
The flange is located at the base of the hydrant and is the main connection point between the hydrant and the rest of the barrel.
The dimensions for the connection of the flange is fully standardized. The height of the flange, on the other hand, is important for the installation of the hydrant. Since speed is crucial for firefighting, the outlets of the hydrant must be tall enough to allow for a full revolution of a hydrant wrench.
Depending on the jurisdiction, the color of fire hydrants can be used to identify the capacity of a particular hydrant.
According to NFPA 291 the recommended practice for color coded capacities is as follows
1500 GPM or more
499 GPM or less
The conventional dry barrel hydrant includes threes outlets: Two 2 1/2” side outlets and one 4” or 6” pumper outlet. The name “pumper” comes from the origins of filling fire pumper trucks. The size and number of outlets are a design choice to limit the capacity of a given hydrant. In some regions only one outlet may be needed.
The stem nut functions as the major port for operating the main valve within the hydrant. The nut is often a pentagon shaped key needing a hydrant wrench to turn. The rotation of this nut turns the operating stem and subsequently rises the and lovers the main valve open or closed.
Unless the branch pipe is restrained, the thrust block is used to support the surrounding soil around the hydrant and prevent hydraulic pressure from causing damage after the valve is opened.
Located at the bottom of a dry barrel hydrant, the valve consists of a plug that raises or lowers to open and close water flow. Opening the valve fills the barrel of the hydrant while simultaneously sealing drain holes at the base of the hydrant. While in the closed position, the valve stopes the passage of water through the rest of the hydrant and re-opens drains to empty the barrel. Depending on the particular hydrant the valve may turn open to the left or the right.
Manufacturers include, but not limited are:
- East Jordan
- S. Pipe
There are three types of valves used in the waterworks industry.
- Gate Valve
- Butterfly Valve
- Check Valve
The most common valve in municipal water works is the gate valve. These valves are simply used to turn water on or off. The most frequently used gate valve in the water main industry is the resilient seat gate valve which replaced the double disc style in the early 1970’s. The available sizes for this valve range from 2-48” and conform to AWWA C-515 specification.
Underground gate valves are normally supplied with a 2” square operating nut marked with either open left or open right arrows Larger sizes are supplied with either worm gear or bevel gearing to assist in the operation of the valve.
A special valve key operator is often needed to open the valve. An adjustable or non-adjustable valve box with a lid marked “water” is supplied to have access to the buried valve.
Gate valves are made from cast iron and are painted with an epoxy coating to prevent rusting, along with stainless steel stem. Nuts and bolts are normally furnished for exposed and non-exposed parts to prevent rusting. The wedge is made of rubber to be fully encapsulated. Gate valves are rated up to 350 PSI while bubble tight rated at 250 PSI. Valves are designed to be able to be maintained in-line operation
Valves are tested for AWWA, UL & FM standards. End configurations are mechanical joint, flange slip-on, and threaded. Different configurations such as MJ X Flange, and Slip-on x Flange are also available.
Tapping Valves (2”-12”) are used with Cast iron or stainless-steel tapping sleeves. These valves have an integral ring on the flange side to mate up with tapping sleeve outlet.
Outside screw & yoke (OS&Y) resilient valves are primarily used in fire protection as well as post indicator valves. They have a plate attached to assemble a post indicator to visually show the position open or closed.
OS&Y valves are supplied in flange configurations for above ground use. The stem rises and lowers as the valve is opened or closed. When the valve is fully opened, the stem will be at its highest point for visual observation.
SPECIFICATION AWWA C509/C515 FOR RESILIENT SEATED GATE VALVE
This specification encompasses the standards for the design, manufacturing and testing of resilient seated gate valves for sizes 2” - 108”.
Gate valves sized between 3” - 72” must follow AWWA C509 and C515. Additional requirements may include ANSI NSF 61 and ANSI NSF 372 certification. Sizes that are larger than 72” are made in compliance with AWWA Standards, where applicable.
Valves between 2” - 48” either have a flange, mechanical joint or flange by mechanical joint end connections. Any valve larger than 54” will include a flanged connection according to ASME B16.1. Valves classified as Class 125 are rated for 250 psi while Class 250 is rated for 600 psi.
Gate valves can either be made with a non-rising stem (NRS) or outside screw and yoke (OS&Y).
Valve testing follows AWWA C509 or C515 specifications.
ASTM A536 Grade 65-45-12 ductile iron is used for the bonnet, body wedge and gland. Stainless steel or bronze is used for the stem and bolts. For sizes between 2”- 48” the wedge is often coated with a synthetic rubber. Valves large than 54” have a mechanically restrained rubber seat around the wedge that is held in place by stainless steel. Most rubber parts are made from either EPDM or other specified elastomer. OS&Y have several gasket rings to protect the packing and a stuffing box. Valves above 30” have stainless steel rollers tracks to maintain a smooth surface between the rubber seat and the iron body.
The internal and external epoxy coating of gate valves follow the certifications set by NSF 61
Another form of valve used in the water transmission is the butterfly valve. This valve is available in 3” - 48”, with mechanical joint, flange, or slip-on end connections. Configurations can be supplied with either 150, 250 or 350 PSI.
Butterfly valve design allows for a cheaper and often more rugged valve. These valves operate under lower torque, eliminating expensive actuation needed for the standard gate valve.
Butterfly valves are especially used for throttling the flow of a pipeline. This is done by leaving a partial opening whereas the gate valve must be either open or closed.
Valves are rated as C-504 with long service life and low maintenance.
Optional equipment can be used for buried service that gives a position indicator that shows that the valve is open or closed at ground line.
Another common above ground valve is the flanged check valve. These valves are designed to keep water from backing up into the municipal water distribution system.
Most check valves utilize gravity and swinging door to close. They can also be supplied with either a lever and weight or a spring design to help with higher pressures. AWWA valves meet C-508 specifications with 125#, 200# or 250# flagged ends certified to ANSI/NSF 61. Check valves can be easily maintained in-line by removing the top plate.
The plug valves are used for dirty liquids, sludge or slurry applications. These conditions lend themselves to generally be used in the wastewater application. These valves can be used above ground or in buried applications. Plug valves can be supplied with a square operating nut or handwheel, depending on needs. Like butterfly valves, these valves can be used to isolate or throttle the line it is servicing. Various material can be used for body, depending on application and media.