Do You Know About Solenoid Valves in Ultrapure Water Equipment?

In ultrapure water equipment, solenoid valves are arguably the most crucial components. Whether acting as inlet, wastewater, flushing, circulation, or water intake valves, their function is essentially to control the flow of water. Our company uses pulse solenoid valves and general-purpose solenoid valves (Airtac, Mingyuan, and household solenoid valves). Different solenoid valves have different working principles and characteristics; understanding these differences is essential for selecting the right valve to meet your requirements.

During production, we encountered situations where water quality failed to meet standards during circulation. After multiple circulation cycles, the water quality could not be optimized. Following this incident, the technical R&D department, production department, and quality department jointly analyzed the problem and identified the root cause. Because the solenoid valve used is a pulse solenoid valve, its working principle is as follows: a positive pulse signal is input to the coil inside the solenoid valve body through a wire. The working magnetic flux generated by the coil causes the moving core to engage, opening the valve. When the positive pulse signal input stops, the moving core releases and returns to its initial state under the action of spring force, closing the valve. There is also a self-holding type, which can maintain its position even after the positive pulse input stops or power is cut off, but requires a negative pulse signal to recover. Because its valve body structure is pilot-operated, when the pulse solenoid valve is used as a circulation solenoid valve, it can lock water in the positive direction, but it lacks the reverse water-locking kinetic energy. Therefore, during circulation, this solenoid valve cannot distinguish between the water before and after circulation, resulting in an inability to optimize water quality. Therefore, only by understanding the working principle and characteristics of each type of solenoid valve can we better select the appropriate solenoid valve for different applications and better meet usage requirements.

Below is an analysis of the working principles and characteristics of several solenoid valves used by our company. Based on our experience with the solenoid valves used so far, they can be divided into two main categories according to their operating mode: direct-acting and pilot-operated. The principles and characteristics of each type are described below:

1. Direct-acting solenoid valve (Airtac general-purpose solenoid valve)

Principle: When energized, the electromagnetic coil of a normally closed direct-acting solenoid valve generates electromagnetic attraction, lifting the valve core and causing the closing element to leave the valve seat, thus opening the valve. When de-energized, the electromagnetic force disappears, and the spring force presses the closing element onto the valve seat, closing the valve. (The normally open type is the opposite.)

Characteristics: It can operate normally under vacuum, negative pressure, and zero pressure difference. It can be installed arbitrarily for DN50 and below, but the solenoid head is relatively large.

2. Pilot-operated solenoid valve (Mingyuan/household solenoid valve, pulse solenoid valve)

Principle: When energized, electromagnetic force drives the solenoid valve to open the pilot valve. The pressure in the upper chamber of the main valve drops rapidly, creating a pressure difference between the upper and lower chambers of the main valve. The medium pressure pushes the main valve closing element upward, opening the valve. When de-energized, the spring force closes the pilot valve, and the inlet medium pressure quickly enters the upper chamber of the main valve through the pilot orifice, creating a pressure difference that closes the main valve.

Features: Small size, low power consumption. However, the differential pressure range is limited and differential pressure conditions must be met. Note: Household solenoid valves are not easy to lock water under reverse high pressure, and pulse solenoid valves cannot lock water under reverse pressure.