Reduced Pressure Zone Device is the type of device that prevents the back flow of water and back siphoning ,hence used in preventing contamination of water supply.The water that has already left the supply may not get back in either through back siphoning or back pressure.RPZD are preferred over air gap devices because of their smaller heads.
These back-flow preventers are categorized into 3 groups,an assembly,a device or a method.There are then eight assemblies and all have two shut of valves with test ports that are properly located into position.
The main advantage of using these assemblies is because they are in a serviceable line and could therefore be repaired without necessarily having to remove them from an already installed assembly.
Benefits and Characteristics of RPZD.
They offer maximum protection against back pressure and siphoning.
They are corrosion resistant and do have a low head loss.
These RPZDs are able to perform well even in temperatures ranging from 1-60 degrees Celsius.
They can withstand pressures that are as high as 1200kPa
They are designed in a line for quick repairs and maintenance.
They only allow inside passage and not an external passage.
Where They are Used
These devices are often used in sewage treatment plants,water supply plants,cooling towers to provide maximum protection from contamination in high hazard places.
How RPZD Works.
The mechanisms in which this highly ingenious device works can be compared to how the heart valve works.It allows water to pass through it ,but closes when pressure comes back from the other side.
In details,it has an outlet shut off valve and an inlet one,4 properly located test cocks,a relief valve component and the first and second check valve components.
Now,assuming water is passing through the system,the inlet shut off valve is opened,water enters the inlet of the assembly of the first check valve.It then enters a relief valve sensing line and moves along up to the elastic element in the relief valve.Pressure builds up in this area and the causes the relief valve stem to compress the relief valve spring therefore making the disc to move and seal the relief valve seat.When the water pressure has already closed this valve,pressure will build up to the next point which will in turn cause the first check to open and allow water to pass through it.The pressure of water will be reduced by the amount of pressure it takes to open the first check.
Once the first check opens,water will pass through it and go ahead to pressurize the area between the two check valves.
When this area is pressurized,it leads to another pressure to the side of the relief valve.
Then when the are between the check valves and the relief side is under pressure,the second check opens and allows water through it,and pressure is reduced.
A perfect RPZD will have the relief valve pressured to close and check valves should be modulated between an opened and closed position.This in turn checks pack pressure and back siphoning
