Abstract: A check valve comprises a plurality of poppets and a plurality of springs for urging the poppets, and the poppets and the springs are coaxially disposed. More specifically, the check valve comprises a case, an outer poppet slidably and sealingly inserted into the case, a first spring disposed between the case and the outer poppet for urging the outer poppet, an inner poppet slidably and sealingly inserted into the outer poppet, and a second spring disposed between the inner poppet and the outer poppet for urging the inner poppet. A check valve is free from clogging of contaminations under the contaminated environments. The check valve can stop flow of fluid when the seat surface or spring is damaged or broken.

Abstract: A back pressure valve accumulates therein a predetermined amount of fluid having pressure higher than a predetermined level.The back pressure valve comprises a casing having a chamber formed therein, which chamber is communicating with an inlet port and an outlet port, a piston which is slidably installed in the casing, an elastic member which urges the piston toward the inlet port, and a relief valve which opens when pressure in the chamber exceeds a predetermined pressure level so as to permit flow of fluid from the inlet port to the outlet port.The back pressure valve further comprises a cylindrical piston which is slidably inserted between an outer periphery of the piston and an inner periphery of the casing, and an outer elastic member which urges the cylindrical piston toward the inlet port.The back pressure valve minimizes occurrence of trouble due to clogging of contaminations though it is simple in construction and inexpensive.

Abstract: A pressure balance type solenoid controlled valve suitable for use under contaminated environments. The valve comprises a body, a solenoid mounted in the body, an armature mounted in the body movably by the solenoid and a poppet valve connected to the armature. The body has a sleeve loosely fitted thereto and a fluid passage formed therein. The poppet valve is provided with a seat portion for switching the fluid passage formed at a front end thereof. The poppet valve is pivotally connected to the armature at a rear end thereof. The poppet valve has an outer diameter substantially equal to a diameter of the seat portion at an intermediate portion between the front end and the rear end. The intermediate portion is slidably inserted into the sleeve. The poppet valve has a passage formed therein for equalizing pressures applied to sides of the sleeve.