Air Flow Control Technology of Air Cooling Heat Pump Unit
In a water pump pipeline system, when the pump is suddenly stopped, the check valve at the pump outlet closes rapidly. This causes an immediate drop in the flow velocity within the pipe downstream of the valve, leading to a backflow and generating an impact pressure. The sudden change in velocity creates a pressure wave that travels quickly through the system, potentially increasing the pressure at the valve’s outlet several times the normal operating pressure. This phenomenon, known as water hammer, can cause severe damage to valves or pipes, resulting in accidents. To prevent such incidents, modern systems use valves with delayed closing mechanisms—such as two-stage controlled butterfly valves, hydraulic control valves with a secondary flap, or slow-closing check valves. These valves delay the closure, allowing some water to flow back through the pump and rotor components, thus relieving pressure. However, this prolonged pressure relief can cause long-term damage to the pump rotor and motor parts due to reverse rotation.
To address these issues, an automatic pressure relief valve has been designed to be installed in a bypass pipe. This valve redirects the backflow to the pump inlet during pressure relief, eliminating the need for the water to pass through the pump rotor. As a result, the problem of pump reversal caused by pressure relief is completely resolved, effectively preventing water hammer.
**1. Structural Design**
As shown in Figure 1, the valve consists of a valve body, a hydraulic chamber, hydraulic lines (a and b), and a hydraulic transmission rod. The valve body is a four-way pipe with a threaded hydraulic transmission rod, a lower valve plate, and an upper valve plate at both ends. The lower part of the valve body is connected to a bottom cover using a connecting screw. Each inlet and outlet on the top and bottom of the valve body is connected to pipelines, with sealing seats placed near the inlets and outlets. The upper valve plate is welded to the hydraulic transmission rod, while the lower valve plate is attached via a nut and thread. The upper part of the valve body is connected to the hydraulic chamber through a flange.
The hydraulic chamber includes a seat, cover, piston, and a diaphragm. The hydraulic chamber seat is secured with a sleeve, screw, and nut, while the piston is located inside the chamber. A sealing O-ring is placed on the piston to isolate the upper and lower chambers. The hydraulic chamber cover has a through hole that connects to hydraulic line a, while the hydraulic chamber seat also has a through hole that connects to hydraulic line b.
O-rings are installed on the upper and lower valve plates, as well as the hydraulic chamber seat sleeve. Gaskets are placed between mating surfaces to prevent leakage. A filter and a micro-control valve are installed in the hydraulic lines to ensure clean fluid flow. A bleed plug is also included on the hydraulic chamber cover to release gas from the upper chamber.
**2. Working Principle and Function**
The bypass pilot relief valve is installed on the bypass line after the check valve on the pump outlet. It functions by redirecting backflow to the pump inlet during pressure relief, thus preventing the flow from passing through the pump rotor. When the pump starts, the pressure in the lower chamber of the hydraulic chamber is higher than that in the upper chamber, causing the piston to move upward and lift the lower valve plate. This allows liquid to flow through the valve and out of the system.
During a power outage, the check valve closes automatically, causing the pressure in the upper chamber to exceed that in the lower chamber. The piston then moves downward, releasing the seal and allowing liquid to flow back into the pump. At the same time, the upper valve plate seals off the flow, completing the pressure relief process. The gaskets and O-rings ensure no leakage occurs, while the adjustable regulating valve controls the pressure relief time, making the system suitable for complex piping networks.
**3. Application**
Three types of pressure relief valves have been developed with diameters of 80mm, 150mm, and 300mm, rated for 1.6MPa. They have been successfully applied in municipal water supply, metallurgical cooling systems, and petrochemical cooling systems. After nearly one year of operation, they have proven effective in eliminating water hammer and solving the issue of long-term backflow impact. The design is feasible, with accurate parameter selection and reliable performance.
This new type of bypass hydraulic control relief valve, installed on the outlet side of the main pipeline check valve, works in conjunction with the check valve to utilize the pressurized liquid for automatic control. It eliminates the problem of pump rotor damage caused by water hammer, and its adjustable closing time makes it suitable for various complex pipeline systems, offering extended application value.
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