Working principle of air conditioning bypass valve

Differential pressure bypass valve is divided into two types: self-operated differential pressure bypass valve and electric differential pressure bypass valve.

Electric pressure difference bypass valve: It controls the bypass flow of chilled water by controlling the opening of the pressure difference bypass valve, so that the pressure difference at both ends of the water supply and return main pipe is constant. It is widely used between water collectors of central air conditioners and between water supply and return of heat pumps, which can effectively keep the equipment from being damaged.

Electric pressure difference bypass valve is often used in gas or liquid system to control the pressure difference between gas or liquid pipeline and circuit. The electric differential pressure bypass valve is installed in the bypass pipeline of the system water pump accessory. When the system differential pressure increases and exceeds the set value of the control valve, the valve will open wider, so that more water will flow through the bypass valve, thus reducing the system differential pressure. On the contrary, the decrease of pressure difference leads to the decrease of valve opening and the increase of system pressure difference.

Self-operated pressure difference bypass valve: The bypass valve is also known as self-operated bypass pressure difference valve and self-operated pressure difference control valve. Self-operated self-pressure difference control valve, in the control range, the automatic valve plug is closed, and when the pressure difference at both ends of the valve exceeds the preset value, the valve plug will automatically open. Under the action of the pressure-sensitive membrane, the opening degree is automatically adjusted to keep the pressure difference at both ends of the valve relatively constant, and the valve works by its own pressure difference, without any external power, with reliable performance.

Self-operated differential pressure control valve is applied to the protection of cold (hot) source units. It is installed on the bypass pipe between the water collector and the water distributor. When the user side runs partially or with variable capacity, the system flow decreases, resulting in an increase in pressure difference. When the pressure difference exceeds the set value, the valve will automatically open, and part of the flow will pass through, so as to ensure that the unit flow is not less than the limit value.??

Self-operated self-pressure difference control valve is applied in central heating system to ensure that the heat dissipation equipment somewhere does not overpressure or empty. For example, the height difference of a system is large, and there is no difference between high and low zones. At this time, if the pressure is set at the high level, the cooling equipment at the low level may burst; If the pressure is set at the low position, it will be emptied at the high position.

In this case, if the heat source is low, the booster pump can be added to the branch pipe of the high zone, and the pressure difference valve of return pipe will increase the pressure in the high zone, and then it will be reduced to the return water pressure in the low zone by the valve. If the heat source is at a high place, it can enter the water supply pipe in the low area and add a pressure differential valve, and add a booster pump to the backwater, so that the circulating water whose pressure is reduced by the valve can be returned to the system.?

Function and Principle of Bypass Valve: The differential pressure bypass valve of air conditioning system is used in the main pipeline between the water collector and water separator of chillers. Its principle is that the differential pressure controller senses the water pressure at both ends of the water collector and water separator, then calculates the difference value according to the measured pressure, and then the differential pressure controller compares the calculated difference value with the preset value to determine the output mode, so as to control the valve to increase or decrease the opening, thereby adjusting the water quantity and achieving the purpose of balancing the water pressure of the host system.?

Function of pressure difference bypass valve: the decrease of chilled water flow rate is quite dangerous for chillers. In the design of evaporator, a constant water flow rate (or a small range of fluctuations) is usually important to ensure the uniformity of water flow rate in evaporator tubes. If the flow rate is reduced, it will inevitably lead to uneven water flow rate, especially at some transitions (such as the head), which will easily slow down the flow rate or even become stagnant "stagnant water". Because the evaporation temperature is extremely low, the low-flow water or "stagnant water" will easily freeze during the continuous refrigeration of evaporator. Therefore, the flow rate of chiller energy is required to be basically constant. On the other hand, from the use requirements of the terminal equipment, the user side requires the water system to operate at a variable amount to change the amount of cooling (heating). The two constitute a pair of contradictions, and the most commonly used method to solve this contradiction is to set a differential pressure bypass valve on the water supply return pipe.

The working principle is that when the system is in the design state and all equipment is running at full capacity, the opening of the differential pressure bypass valve is zero (no bypass water flow). At this time, the pressure difference at the interface between the two ends of the differential pressure controller (also known as the user side supply and return water pressure difference) P0 is the set pressure difference of the controller. When the end load decreases, the two-way valve at the end will be turned off, and the pressure difference P0 of supply and return water will increase and exceed the set value. Under the action of the pressure difference controller, the bypass valve will automatically open. As the bypass valve is connected in parallel with the water system at the user side, its opening will decrease the pressure difference P0 of supply and return water until it reaches P0, and then it will stop. Part of the water will flow through the bypass valve and directly enter the return pipe, where it will be mixed with the return water at the user side and then enter the water pump and chiller, so that the amount of water passing through the chiller will not change.