Explaining the Principles of Different Types of Normally Open Solenoid Valves

At present, normally open solenoid valves have numerous models and functions, and they work in all aspects. However, they are divided into numerous categories only because the products differ, such as air-conditioning normally open solenoid valves, zero-pressure normally open solenoid valves, and camshaft normally open solenoid valves. But in fact, there are not many categories that can be classified; from the perspective of their motion mode, they only need to be divided into three types, namely: direct-acting, step-by-step, and pilot. According to their own differences they can be further divided into other types, all of which can be subdivided. However, these different classifications have completely different principles and uses in different aspects, so this issue briefly explains the content in this regard.

I. Direct-acting normally open solenoid valve

Working principle: when a flanged 2-way 2-position solenoid valve starts, the electromagnetic coil generates an electromagnetic suction force that lifts the valve body upward, thereby separating the seal on the valve seat from the valve seat and opening the valve plate; when the power is cut off, the force of the electromagnetic wave weakens, and the valve core seal is also affected by elastic force, causing the valve seat to close. (Relative to the conventional one.)

Features: suitable for zero pressure, negative pressure, pressure difference, and larger valve diameter. Such as an electromagnetic high-pressure valve.

II. Step-by-step direct-acting normally open solenoid valve (i.e., reverse control)

Its working principle is: a combination of direct drive and pilot. For example, when an American-standard stainless steel ball valve starts, the normally open solenoid valve first opens the sub-valve; at this time the pressure in the lower cavity of the main valve is greater than the pressure in the upper cavity, thus opening the valve under the action of high pressure and electromagnetic force; when the power is cut off, the sub-valve uses the pressure of the spring or the medium to open the valve.

Features: under zero pressure difference or near a certain pressure, the working pressure usually does not exceed 0.6 MPa, but because the electromagnetic head's power ratio and volume are relatively large, vertical installation is required.

III. Pilot normally open solenoid valve

Working principle: during the starting process, it is opened through a high-temperature normally open solenoid valve, thereby rapidly reducing the pressure in the upper cavity of the main valve, thus forming a pressure difference between the upper and lower cavities of the main valve, and pushing the main valve closing element upward through the pressure of the medium, thereby opening the valve; when power is cut off, the elasticity of the valve core is closed, and the inlet pressure of the medium quickly flows from the throttle hole into the upper cavity of the main valve, causing a pressure difference in the upper cavity, thereby closing the main valve.