Selection Criteria For Continuous Valves - Burkert 8630 Operating Instructions Manual

G R (A
ENERAL ULES

Selection criteria for continuous valves

The following criteria are of decisive importance for optimal control behaviour and attainment of the
maximum flow rate through the valve:
• Correct choice of flow coefficient, which is defined essential by the size of the valve;
• Good matching of the valve size to the pressure conditions, taking into consideration the other flow
resistances in the system.
Dimensioning guidelines can be given on the basis of the flow coefficient (k
standardized conditions with respect to pressure, temperature and media properties.
The k value is defined as the flow rate in m
v
Dp of 1 bar and a temperature of 20°C.
With continuous valves the " k
continuous valve is fully open.
Depending on the specified data, the following cases must be distinguished on selection of a valve:
a) The pressures before and after the valve p
Q is to be attained:
max
The required k
=
k Q
VS max
where:
k is the flow coefficient of the continuous valve when fully open [m³/h]
VS
Q is the maximum volumetric flow rate [m³/h]
max
∆p
= 1 bar; the pressure drop over the valve as in the definintion of k
0
r = 1000 kg/m³; the density of water as in the definition of k
0
∆p
is the pressure drop over the valve [bar] and
r is the density of the medium [kg/m³]
b) The pressures at the inlet and outlet of the overall system (p
desired maximum flow rate Q
Step 1: Calculate the flow coefficient of the overall system k
Step 2: Measure the flow rate through the system without the continuous valve
(e.g. by short-circuiting the piping where the vale is installed).
Step 3: Calculate the flow coefficient of the system without the continuous valve (k
equation (1).
Step 4: Calculate the required k
=
k
VS
k
Vges
158 - 8630
)
PPENDIX
value" is additionally used. This specifies the k
vs
value is obtained from:
vs
ρ
∆
p
⋅ 0 ⋅
(1)
ρ
∆
p
0
is to be attained:
max
VS
1
(2)
1 1
−
2 2
k
Va
3
/h of wasser through a component at a pressure difference
and p are known at which the desired maximum flow rate
1 2
and p
1
value of the continuous valve ( k
). The k value refers to the
v v
value when the
v
V
V
), are known at which the
2
from equation (1).
Vges
Va
) from equation (2).
VS
) from