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Valve Terms
  • Breaking Pressure:
    The minimum pressure required to produce flow through a valve.
  • Duty Cycle:
    100% duty cycle is defined as continuous operation without any damage occurring. For intermittent duty cycle (<100%), alternate energized and de-energized state at regular intervals to allow the valve to completely cool down to room temperature. 
    F = active concentration / total concentration
  • Flow Patterns:
    A diagram showing how flow can be directed using a particular valve. (See the “Flow Patterns” box below for further explanation.)
  • Normally Closed:
    Valve stays closed in de-energized state; opens when energized.
  • Normally Open:
    Valve stays open in de-energized state; closes when energized.
  • Pressure Differential or Pressure Drop:
    The difference between the inlet and the outlet pressure through a valve. The outlet pressure is lower than the inlet pressure due to the restriction caused by the valve.
  • Three-Way Valve:
    Has three ports. Depending on the particular valve, all three ports may be open, two ports may be open, or all ports may be closed.
  • Two-Way Valve:
    Has a single inlet port and a single outlet port.

 

Selecting your Valve
  1. Choose a valve type depending on your application. Our manual valve selection includes ball, check, diaphragm, elliptic, metering, needle, pinch, plug, pressure relief, and stopcock valves. Our actuated valve selection includes electrically actuated ball, elliptic, pinch, proportioning, and general-purpose solenoid valves.

  2. Consider your fluid type (liquid or gas) and its characteristics to determine compatible valve materials. PTFE withstands many harsh or corrosive chemicals. For safety reasons, always use metal valves for pressurized gases.

  3. Determine the temperature, pressure, and flow rate under which your valve will be operating. In general, metal valves withstand higher temperatures and pressures than plastic valves.

  4. For solenoid valves, consider response time and length of time valve will be energized. Continuous (100%) duty solenoid valves are best for frequent on/off cycling. Choose normally closed or normally open depending on the state the valve will be in most often.

  5. Consider your maintenance requirements. Ball valves resist plugging and are easiest to service.

Valve Types
  • Angle-Seat Valves:
    Utilize an ultra-compact actuator to move a piston back and forth within the valve body. On/off control and continuous control designs are available for gases, steam, and liquids. The construction of the body allows extremely high flow rates, particularly in comparison to conventional globe valves.
  • Ball Valves:
    Designed primarily for on/off service. These valves contain a ball with a hole through it. A handle or electric actuator rotates the ball 90, turning the flow on or off. Use plastic ball valves for liquid applications only.
  • Butterfly Valves:
    Designed primarily for on/off service. These valves have low pressure drops and are self-sealing so they donÕt require an additonal flange gasket for installation. For pipe sizes ranging from 1.5" to 12" dia.
  • Check Valves:
    Self-actuated valves designed to prevent fluid from flowing backward into your system. Flow forces a ball or disk in one direction to open the valve; when flow stops, the ball or disk seats to close the valve.
  • Diaphragm Valves:
    Use a flexible diaphragm to shut off flowÑcenter of the diaphragm is pushed down into a seat. Use these valves for fluids that are dirty or have a high particulate content.
  • Elliptic Valves:
    Similar to ball valves except elliptic valves use an elliptic O-ring to seal the cylinder during rotation. The seal design makes these valves ideal for vacuum applications.
  • Manifold Valves:
    Have one common port to two or more additional ports. For mixing, use the common port as the outlet; for distributing, use the common port as the inlet.
  • Metering Valves:
    Multi-turn valves designed to regulate the flow of fluid. These valves generally have low flow rates and high pressure differentials.
  • Needle Valves:
    Feature the most accurate flow control among the valves we offer. They are an excellent choice for precise metering of liquids or gases.
  • Pinch Valves:
    Use solenoid to squeeze shut a piece of tubing. Fluid contacts only the tubingÑideal for your high-purity fluid applications.
  • Plug Valves:
    Used primarily for on/off service. Controls flow using a plug with a hole through it. Plugs can be made of rigid materials such as PTFE¨, making them ideal for high-purity applications.
  • Pressure Valves:
    Designed to control or limit pressureÑnot flowÑin a system. These self-actuating valves will either open a relief port or bypass the fluid when a preset limit is reached.
  • Proportioning Valves:
    Designed to produce variable flow rates. Valves open and close in proportion to the signal from your controller.
  • Sample Valves:
    Special three-way valve designed to tap off a portion of the main flow for sampling purposes.
  • Sanitary Valves:
    Feature Tri-Clamp connections and 316 stainless steel body construction for sanitary and high purity applications.
  • Solenoid Valves (Direct Lift):
    Use a plunger that is actuated to open or close the fluid path. These valves usually have low flow rates and high differential pressure drops. They generally have quicker response time than pilot-operated valves.
  • Solenoid Valves (Pilot-Operated):
    Utilize pressure created by air or liquids for actuation purposes. These valves are either piston or diaphragm types and require differential pressure to keep valve closed. Because they donÕt have a plunger, they are usually available in larger orifice sizes than direct lift valves.
  • Stopcocks:
    Similar to ball valves except stopcocks are much smaller in size. Primarily used in the laboratory for on/off control of flow or as a crude regulation of flow rate.

Reference source:  http://www.coleparmer.com/TechLibraryArticle/703