The name 'Landing valves' were used to describe valves for fire fighting provided on Risers in buildings, as these were typically located in Staircase landings to allow easy access to Fire fighters. Hence, the name 'Landing valve' came to be associated with these type of valves in buildings. As firewater systems for municipal/ industrial applications are typically called hydrant systems, the term 'Hydrant valves' was used to describe the valves fitted on the Hydrant stand posts in such systems. Both terms actually refer to the same type of valve, though the term 'Landing valve' is more associated with building applications.
Though the basic function of hydrant valves remains the same, depending upon application/ location/ code requirements, different designs and sizes are available. Typically, Hydrant inlets can be flanged or threaded (threaded being used for low pressure applications, typically upto 7 kg/cm2). Inlet sizes could vary from 100 NB (4") size to 50NB (2") size. Similarly outlets can be have instantaneous/ threaded/ storz couplings, and sizes can vary from 75 NB (3") to 38 NB (1.5").
As mentioned above, hydrant valve inlets can be threaded or flanged. Present BIS standards do not specify threaded connections, however same are being commonly used in many regions and countries around the world.
A double headed hydrant valve consists of a common inlet and body with two outlets. This will have two bonnets, stems and wheels. Double headed hydrant valves were earlier being used where higher flows were required due to severe hazards i.e. you could connect two hoses from the double headed hydrant.
Single headed hydrant valves are standard hydrant valves with a single inlet and single outlet. A double headed hydrant post is fitted with two separate single hydrant valves, allowing two hoses to be connected from the same hydrant post.
Due to the larger body of double headed hydrant valves, there are safety concerns, and nowadays, double hydrant posts with two separate single hydrant valves are used instead.
Normally, fire fighting equipment to be connected to and operated from a hydrant valve is designed for 100 psi (approx 7 kg/cm2) pressure. Hence the normal operating pressure is approx 7 kg/cm2. However, this may vary for different applications for e.g. on large industrial complexes, the operating pressue may be in the range of 10-11 kg/cm2. Similarly, if small diameter hoses (38 mm e being used with hydrants, the pressure may be 4 to 5 kg/cm2.
Flow requirements from hydrants depend on the type of application and the standard fire fighting equipment (branches) which will be connected to the hydrant. This could vary from approximately 2200 lpm (for a double headed hydrant) to 600 lpm for hydrants having 38 NB (1.5") outlets.
Most standards around the world, including BIS, allow the use of different materials for construction for hydrant valves, which include Bronze, Aluminium, Stainless Steel. The main requirements are mechanical strength, corrosion resistance and suitability to application.
Stainless steel (SS) has higher mechanical (tensile) strength as compared to Bronze, hence SS Hydrant valves can withstand higher working pressures as compared to Bronze valves. Stainless steel is non corrosive, and at the same time, can survive harsh industrial environments. Stainless steel, unlike Bronze, has a low resale value, and this reduces theft of the valve parts, which is common with Bronze valves. Cost of Stainless steel and bronze valves are comparable at present marketrates, however due to its durability and long life, the cost of Stainless Steel valves is actually much lower over its entire working life.
When installing hydrant valves, ensure the following –
- Ensure that the mating flange of the hydrant post is matching to the valve inlet flange.
- Orientation of hydrant valve outlet should be as per standard practices and should allow easy connection of hoses.
- Use approved gasket between flanges, and good quality nuts/ bolts
- Ensure minimum height of 750 mm from grade level.
- Ensure that the hydrant valve rated working pressure is matching to the hydrant system line pressure. If hydrant system pressure is higher, ensure that the hydrant valves are rated for a higher pressure, which matches system pressure.
- If Orifice plates are required to be used, ensure that these are of standard size, and provided by the original supplier. Installation of orifice plates should be as per standard practices.
Proper operation of hydrant valves will result in a long and useful life, and at the same time, will ensure that the valve gives effective service when required to do so in an emergency. Certain points to be kept in mind while operating hydrant valves –
- Ensure that operators are familiar with operation of the hydrant i.e. direction for opening/ closing.
- Open and close the valve slowly – this will prevent water hammer, and ensure safety of operator and equipment.
- Do not overtighten the valve (or use spanners) when closing. If valve leaks after closing, it means that the seat washer is not sealing against its seat. This could be due to foreign objects, or wear and tear of washer. Overtightening may damage the threads, bonnet and result in failure of hydrant body.
Hydrant valves, if well designed and manufactured as per quality standards, require little maintenance. Proper periodic cleaning and light greasing of stud threads, and light oiling of the lug will ensure proper operation. Normal parts which can require replacement are the rubber washer (hydrant outlet), seat washer and the gland packing. Use standard washers, if replacement is required.
Though marked/ approved/ listed hydrant valves may look similar in design/ shape, the component size and/ or thread types may differ for different brands. Using externally fabricated/ manufactured parts may also be unsafe, as they may not have the same material properties. Hence it is advisable to use spare parts from the same supplier of the hydrant valve.
Underground Fire hydrants or flush type hydrants are used in certain parts of the world, which experience extremely cold weather (and water in above ground hydrants can freeze). They are also suitable for areas like Air fields where installation of normal hydrants is not possible. The Hydrant outlet is just below the surface of the ground protected by a cover, which is flush with the pavement, and so does not interfere with the aboveground operations.
For operating these hydrants, stand pipes are connected to the outlet of the underground hydrants, and hoses can then be connected to the outlet of the stand pipes.