From the spool suffered unbalanced force

The adjustment mechanism of the valve body has two types of unbalanced and balanced. The balanced spool is a balance hole on the spool spool when the spool moves the spool, the lower part of the balanced hole connection, therefore, the pressure difference across the vast majority of offset, which reduces unbalanced force on the spool, balanced spool need to balance the chamber, therefore, need sealing device seals. According to the type of the flow of the pressure balanced spool valve pressure (the center outward flow)shut off solenoid valve  can also be a pressure valve (external to the center of flow). The balanced spool can be used for the sleeve structure of the valve body, can also be used for the valve body of the plunger structure. Imbalance on both sides of the spool control valve and pressure valve, spool suffered unbalanced force, the same caliber control valve requires greater thrust of the implementing agencies to operate.flange solenoid valve