The law "The more the better" does
not always work. In DBN B.2.5-64: 2012 it is indicate that the pressure in the
water supply system should not exceed a value of 4.5 bar. This is necessary for
the stable operation of sanitary equipment and household appliances. If this
value is exceed, the pressure reducer valve should be install. Today we will
talk about them.
Base information
The name of this armature comes from the
English word "reduce". Accordingly, the main task of the pressure
reduce valve (PRV) is to reduce the water pressure. 95% of the gear units have
a tuning screw or knob for setting the required pressure. To make the correct
adjustment, you need a pressure gauge. Some models are equipped with gauges at
once, but for the majority, it must be purchased separately.
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| Pict.2 The appearance of the piston PRV |
Principle of operation
PRV works on the principle of "after
themselves". Water first passes through the working opening of the valve
(throttle), and then acts on the working mechanism (piston or membrane). If the
pressure is higher than the tuning, the choke starts to close (create more
resistance to the flow of water). And so on until the pressure after the
throttle is equal to the tuning. The scheme of work is in pict. 3.
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| Pict.3 Pistone PRV |
Coefficient of reduction
Among the many characteristics and parameters
of water pressure reducers, there is the notion of "reduction
coefficient". This ratio is the input and output pressure. It must not
exceed 2.5. Very few people pay attention to it. In addition, often choose the
wrong gearbox size or setting. As a result, the effect of cavitation occurs.
Which leads to premature failure of the reinforcement.
Example.
The inlet pressure is 8.5 bar
Desired outlet pressure - 1,5 bar
To avoid cavitation, the working point should
be in the green zone (pict. 4).
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| Pict.4 Cavitation diagram |
Based on the values of the example, the
operating point falls into the cavitation zone (point 3).
The reduction ratio is 8.5: 1.5 = 5.7 (which is
much more than 2.5).
The way out is to install 2 reducers.
The first reduction is 8.5: 3.5 = 2.4 (the
reduction ratio is less than 2.5)
The second decrease is 3.5: 1.5 = 2.3 (the
reduction ratio is less than 2.5).
Types of reducers
By design, water reducers are piston and diaphragm.
The main difference in the working mechanism, which tracks the water pressure.
The design of the piston type shown in pict. 3 (see above). The diaphragm reducer
have shown in Fig.5.
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| Pict.5 Membrane PRV |
Membrane PRV have many advantages over piston
valves.
1. Accuracy
of work. This is due to the large number of friction parts of the working
mechanism of the piston reducer. Moreover, the longer such a reducer works, the
better its accuracy. The membrane responds better to pressure changes.
2. The
durability of the diaphragm reducers is higher for the same reason. The
parts of the piston valve wear out more quickly because of the frictional
force.
3. Work
in both static and dynamic mode.
The dynamic mode is when there is a tap (water
flow). Static - when the flow of water is static (does not flow). Piston PRV
works better dynamically. When moving to "statics", it is possible to
hang pressure.
It is connect with the main negative from the
use of such fittings. Although not always the problem is only in them.
For example, when water comes into the
apartment with a temperature lower than room temperature. It starts to heat up.
In addition, with the expansion there is an increase in pressure.
4. It is
better to work with imperfectly clean water. A common cause of failure of
piston PRV is the sticking of the saddle, piston and other mechanisms. The
significance of this problem increases when water is contaminated. Therefore, a
filter must be place in front of the PRV.
Membrane, not so prone to sticking. In addition,
most of membrane pressure valves have a built-in filter.
Selection
In addition to the design (piston, membrane)
and the reduction ratio, (it should be less than 2.5), when selecting a water
reducer, it is necessary to pay attention to some other things.
The size determination should be make not from
the size of the thread, but from the capacity of the reinforcement. See Table
1.
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| Table 1. Capacity and sizes of PRV |
An
important aspect of choice is the manufacturer.
The best
proposals for piston reducers are offer by Italian companies - Itap, Giacomini,
Tiemme, etc. (see pict. 6 and table 2).
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| Pict. 6. Piston PRVs of different manufacturers |
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| Table 2. Technical characteristics of the piston PRV |
German and Italian brands are leading the
market for membrane reduction valves. The real hits are the products of
Honeywell and Caleffi.
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| Pict.7 Membarne PRVs of different brands |
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| Table 3. Technical characteristics of the membrane PRVs |
Benefit
Reducer is
useful not only because it reduces water pressure, but also as an element of
safety of the water supply. It partially protects from a water hammer.
Also, due
to pressure reduction, the reducer reduces water consumption. For example,
reducing the pressure from 5 bar to 2.5, reduces the water flow to 30%.
Significant resource savings!
So if you
still do not have a PRVat home - run to the store and buy)
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