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Our policy is one of continued research and development. We therefore reserve the right to amend, without notice, the specifications given in this document. © 2015 Norgren, Inc. Simplified Valve Circuit Guide 1 Compressed Air Valves Directional control valves start, stop or change the direction of flow in compressed air applications. Many manufacturing companies apply compressed air as the power to operate tools and equipment which are used to make the products they offer.To understand the different applications of compressed air and how valves are used, one must first have a knowledge of the kinds and types of valves used by industries. Valves are designed for different applications and a factory may use several different types of valves with each being suited for a particular job. These designs fall into the following categories: spool – bonded and lapped; poppet; a combination of spool and poppet; sliding seal; rotary and diaphragm. The two types of spool (bonded and lapped) and the poppet are the most common designs in use. Of these, Norgren makes valves using the packed and bonded spools and the poppet design. Bonded spool valves use an elastomer to seal against pressure. Bonded spools allow practically no leakage, can be used in three-position applications, and the standard valve goes through a blocked center, which prevents blowby from the exhaust ports when changing from one flow pattern to another.. Spool valves are tolerant of dirt and compressor varnish and when lubricated properly, will cycle for millions of operations. Poppet valves use a large poppet seal and operate much the same way as a home water faucet. The seal surface moves perpendicular to the valve area and pushes against an annular ridge for positive sealing. Poppet valves are fast, rugged, and known for their ability to operate under adverse conditions. Spool valves are available in 3-way and 4-way configurations. A 3-way spool valve can be used as a 2-way valve by blocking one port. Poppet valves are made in 2-way, 3-way, and 4-way configurations. Valve Operation Two Way Valves Two-way valves turn air on and off in applications such as shop air, branch airlines, supply pressure to systems, and supply air to tools, motors and similar equipment. Two-way valves can also be used as vent valves. Poppet valve, 2-way, 2-port Normally closed 2-way valves block inlet flow when in the unactuated position. Inlet flow is passing when actuated. Note: Valve symbols always show the unactuated position in the lower block N.C. 2-WAY SYMBOL ACTUATED POSITION UNACTUATED POSITION IN OUT