The fire hydrant is a crucial part of the water supply system for firefighters. It provides water in the majority of areas that have water service. There are multiple types of fire hydrants in use depending on climate and needs. This is a look at primarily United States fire hydrants, the wet barrel, dry barrel, and dry hydrant.
About this creation
In times past, firemen used to drill holes into the wooden water mains to supply their hoses with water. When the fire was extinguished, they placed wooden plugs back in, coining the term “fire plug”. Over time, the wooden mains were upgraded to metal, necessitating a new way of accessing them in emergency situations. Thus, the fire hydrant was invented.
The wet barrel hydrant is always full of water. It has multiple ports on it, each with its own valve. Wet barrel hydrants are used in areas where freezing is not an issue. They offer superior flexibility on the fire scene, with only minimal additional effort.
The dry barrel hydrant does not have water in it most of the time. The water is controlled by a single valve that is deep in the ground, under the frost line. The valve is controlled from the top of the stem. Once the valve is opened, additional ports cannot be used without turning the hydrant off. Once the valve is closed after being used, the barrel of the hydrant slowly drains through weep holes. This creates a suction that can be felt if one covers a port with their hand. Dry barrel hydrants are used in areas where freezing is a concern. When opening a dry barrel hydrant, it is best to open it, flow some water, close it, connect the hose, and finally open it again for use. This allows one to ensure no debris has been placed in the hydrant that may affect the pump.
Dry hydrants are not pressurized by a water system. They are designed to allow an apparatus to draft from a body of water without having to get close to it and risk damage. Hard suction is needed to connect a dry hydrant to the intake port of an apparatus. The drafting ability of the pump is crucial to how high above the water level one can be. Strainers are installed in the body of water to prevent debris from entering the pump.
Per National Fire Protection Association 291 has guidelines concerning the paint scheme of fire hydrants. The primary barrel color is based off the type of system it is. Municipal systems should be yellow, and private systems red. The top of the hydrant is color coded to the flow rate of the hydrant. Class AA hydrants flow 1,500 GPM or more and are colored light blue. Class A hydrants flow 1,000-1,499 GPM and are colored green. Class B hydrants flow 500-999 GPM and are colored orange. Class C hydrants flow less than 500 GPM and are colored red. Hydrants that have black tops are not in service. The port covers should be colored according to the same system to determine flow rate from each port. An alternative option is to paint the ports according to the pressure each has. Green port caps are 120 PSI and above. These need to be handled with caution due to their pressure. Orange port caps are 50-120 PSI. Red are below 50 PSI, and must be drafted from to maintain adequate water flow. Hydrants that do not flow potable water are to be painted purple on top.
Most hydrants have a combination of 2 ˝ inch ports and a “steamer” port of either 4 or 5 inches in diameter. The “steamer” port may either be threaded or a Storz quick connect. The valve control nut is normally five sided. Hydrants are connected to the ground piping with a series of sheer bolts that are designed to break away if the hydrant is hit, minimizing damage to the hydrant. On wet barrel systems, the water main must then be turned off; whereas on a dry barrel system, the water will not flow.
This image shows the underground part of the dry barrel hydrant and the dry hydrant.
Here we have the five cap colors as prescribed in NFPA 291.
In this close up, we see two dry barrel hydrants, a wet barrel, and the dry hydrant.
A brush truck is filling off a dry barrel hydrant.
A dry barrel hydrant has been sheered from its pipe, with no appreciable damage.