Because the coil static characteristic is exponential, in order to achieve good control effect, the logarithmic curve regulating valve is usually used. Only by guaranteeing a certain degree of valve weight can the actual curve of the valve meet the requirements. Because the coil static characteristics are related to the temperature difference of water supply, small temperature difference is more sensitive to this problem, so this problem is particularly important in summer air conditioning design, otherwise, the system stability time is too long.
Ideal flow characteristics of valves
1. Straight-line type: The change of flow caused by the change of unit stroke is equal.
2. Parabola: The flow characteristic is a quadratic parabola, which is between straight line and equal percentage characteristic.
3. Equal Percentage Type: The same stroke has little change in flow rate at small opening and large change in flow rate at large opening.
4. Quick-opening type: when the stroke is small, the flow rate is relatively large, and the valid stroke of the valve is less than d/4, which is mostly used to shut off the valve. Realization of Ideal Flow Characteristics of Valves: Core Shape
(1) Linear Characteristic Valve Core
(2) Valve spool with equal percentage characteristics
(3) Quick-opening characteristic spool
(4) Parabolic characteristic spool
(5) Valve spool with equal percentage characteristics (open shape)
(6) Linear characteristic spool (open shape)
The Definition of Value Degree and Value Degree
Valve power is the means to achieve hydraulic balance.
1.Static balanced hydraulic calculation and reasonable piping. Same program. Static balance valve. Dynamic differential pressure balance valve or dynamic flow balance valve.
2. Dynamic balance dynamic differential pressure balance valve is the only way to solve dynamic misalignment.
Classification of Balance Valves
1. Static balancing valve manual balancing valve: also known as static balancing valve, balancing valve, by manually adjusting the opening of the valve to change the KV value of the valve, consumption of excess pressure difference, measurement of flow through the valve and pressure drop.
2. Dynamic balancing valve dynamic flow balancing valve: also known as dynamic balancing valve, self-operated flow control valve, in a certain range of pressure to maintain flow dynamic constant (in an interval). Dynamic differential pressure balancing valve: also known as differential pressure controller, to maintain the differential pressure in a certain range of dynamic constant (in an interval).
Manual Balance Valve
Principle: By rotating the handle to adjust the movement of the spool, the Kv value of the valve can be changed. The pressure drop and flow through the valve can be measured by connecting the pressure measuring points at both ends of the valve with a special instrument, and the opening of the valve can be locked.
Functions:
1. Regulating valve function, accurately adjust KV value.
2. It has the function of shutting off and measuring the pressure drop and flow rate of the valve.
Function: Consumption of excess pressure difference, so that the pipeline flow and pressure drop are consistent with the design value, flow measurement.
Installation location
Fixed flow system piping, step by step installation, from the end of the branch to the pump outlet of each branch.
In the large branch of the variable flow system (only when the pressure difference on the branch road with the dynamic differential pressure balancing valve is greater than the control pressure difference of the dynamic differential pressure balancing valve), the dynamic differential pressure balancing valve is installed at the end.
Installation of water supply pipe or return pipe is acceptable. The difference is that when installed in water supply pipe, the working pressure of manual balance valve is greater than that of return pipe installation, but the working pressure of end equipment and electric control valve is just the opposite.
Notices for Selection and Use
Type selection:
According to the Kv value, the Kv value of the selected valve is larger than the design value.
The minimum opening is more than 20% of the total trip.
Valve minimum pressure drop greater than 3KPa
Use precautions:
A. Closing valves such as butterfly valves, gate valves, globe valves and ball valves should not be used instead of manual control valves. The valve curve of turn-off type is up-throw curve, which has poor adjustment sensitivity, while the characteristic curve of manual balancing valve is close to linear characteristic and has high adjustment sensitivity.
B. Should not be installed in series, that is, the same loop should not be used to install manual balance valves at the same time.
C. System debugging is very complex, which often requires professional debugging companies to debug.
Debugging Procedures of Manual Balance Valve
1. Number of manual balancing valves for trunk, riser, branch and end
2. Calculate the flow ratio of each riser and find out the riser with the maximum flow ratio, as shown in Fig. lambda 1.
3. Calculate the flow ratio of each branch and find out the branch with the maximum flow ratio, as shown in Fig. lambda 1.
4. Calculate the flow ratio of each end pipe and find the end with the minimum flow ratio, as shown in Figure lambda 1, to lock the valve.
5. Lock the valve after adjusting the flow ratio of each valve and the minimum end flow ratio in turn.
6. Adjust the manual balancing valves of the main pipe and branch pipe in turn. The method is the same until the completion.
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