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Grant Phipps managing director of Watts UK explains
how legislation allows installers freedom to fit PRZ valves
to avoid backflow prevention.
Watts Industries distribute and manufacture controls that
regulate air, gas, water, steam and oil for temperature pressure
or flow. Watts are the leading manufacture in the World of
backflow prevention devices. |
| Backflow - a reversal of the normal flow of water
in a pipe system - can have comical results. In the late 1960s
wine flowed through the taps of the surprised and delighted
residents of Cincinnati, USA, when a local winery left a water
supply valve open after flushing its fermentation tanks. But
backflow can also be dangerous, causing drinking water contamination…
or worse. For example, a maintenance man connected a large liquid
petroleum gas tank to a water main to wash it out. Unbeknown
to him, there was still gas under pressure in the tank. By opening
the water supply valve, he back pressurised the water supply
main with gas, causing three nearby houses to explode. There
are horror stories in the hvac market too. In one case, water
backflowed into the air conditioning system of a Philadelphia
hotel, resulting in conditions that fostered the growth of the
bacteria that cause Legionnaires' Disease.
These examples are extreme. But backflow is a real threat
- the US Environmental Protection Agency reckons that at least
100,000 cases of cross contamination occur in the USA every
day. That makes it a pressing health & safety issue, and
its prevention a priority.
Backflow is caused by one of two factors
- Back siphonage, which occurs when the pressure on the
supply end of a water pipe drops dramatically. This causes
a vacuum which can suck fluids back through connections
upstream thus contaminating the water system.
- Back pressure, the result of reversed water pressure on
an outlet from a water main connection exceeding the mains
supply pressure.
One solution to these problems is the reduced pressure zone
(RPZ) valve. It employs spring check valves create an intermediate
zone of pressure that is lower than the supply pressure. If
back pressure builds up and the outlet check valve fails to
hold, the intermediate zone will pressurise and cause a relief
valve to open, draining the entire assembly, thus preventing
possible contamination back into the supply.
Installers in the USA have used RPZ valves since the early
1970s when Watts Industries launched its 909 RPZ. Now the
British Government has decided to allow their use in this
country. The new Water Regulations which replace the Model
Water Byelaws free installers to fit RPZ valves here for the
first time.
Until these regulations, UK installers have had to install
a break tank with a ball valve. However, pressure is lost
from the mains with this arrangement so a pump also has to
be fitted complete with a level switch to control the pump.
This is complex, bulky and expensive, compared with the RPZ
valve.
The RPZ valve can only be operated once its type of protective
use has been approved by the local Water Regulations Inspector
and its correct fitting and operation has been independently
checked by one of the 150+ RPZ-licensed inspectors operating
in the UK. However, its simplicity, low cost compared to break
tanks and ease of installation make it an attractive option
for installers |
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Series 009 RPZ
Watts offers two versions - the 009 with an inlet/outlet
connection up to 3in, and the 909 with an inlet/outlet connection
up to 10in. The company holds permanent stocks of the smaller
versions, and ensures significantly low lead times for the
remainder. Watts is a pioneer in the development of the RPZ
valve, and has proved its commitment with the recent acquisition
of Ames Valves, another major player in this market. |
