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Salt Lake Valve & Fitting Co.

Your Authorized Swagelok Sales and Service Center

Common Regulator Terms & Definitions - sorted alphabetically

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  • Accumulation: the increase in inlet pressure required to obtain a specified flow rate for a back-pressure regulator.
  • Back-Pressure Regulator: back-pressure regulators control inlet pressure by balancing an adjustable spring force against the force of the inlet pressure. The spring force is adjusted by turning the stem/ handle, which sets the desired inlet pressure. When the force caused by the inlet pressure rises above the force of the spring, the regulator opens until the spring force and inlet pressure are balanced again.
  • Bulk Distribution Regulator: a regulator designed with high-flow capabilities - Swagelok's RHPS Series
  • Choke Flow Range: when a regulator is in the fully open position and is no longer regulating pressure.
  • Controlling Element (Main Valve, Valve Stem or Poppet): governs flow by moving into and out of the orifice. Common design types are balanced or unbalanced.
  • Creep: an increase in outlet pressure that occurs when pressure escapes, even though the Controlling Element is closed. Usually a result of particulates in the process stream which can nick the sealing surface of the seat which can cause minor imperfections in the sealing surface. Any other damage to the Controlling Element or the seat can also cause creep. Upstream filtration can help remove particulates from the process stream before entering the regulator. Some regulators include a built-in filter upstream of the seat for this very purpose. Also, regulators should not be used as a shut off device.
  • Droop: describes the drop in outlet pressure, below the original set-point, as flow increases.
  • Hysteresis: the difference between flow curves for increasing and decreasing flow.
  • Inlet: where fluid enters the regulator on the upstream side.
  • Inlet Pressure: the pressure of the upstream connection of a regulator. Typical units of measure are psig, bar, or pascal. When selecting a regulator the inlet pressure is typically matched to the maximum supply pressure.
  • Loading Element: component of the regulator that exerts force on the Sensing Element to counterbalance the pressure of the fluid inside the chamber. Common design types are spring-loaded, dome-loaded, and a combination of the two.
  • Lockup: occurs when the downstream components are shut off. As pressure builds it forces the poppet to seat itself and close off inlet pressure. The pressure at which the regulator shuts off is known as lockup, and the pressure on the outlet side will be slightly higher than the set pressure of the regulator.
  • Orifice: area through which fluid is directed inside the regulator.
  • Outlet: where fluid exits the regulator on the downstream side.
  • Outlet Pressure: the pressure of the downstream connection of a regulator. Typical units of measure are psig, bar, or pascal. 
  • Point-of-Use Regulator: a regulator designed with high sensitivity and accuracy capabilities - Swagelok's K Series
  • Pressure Control Range: the range of pressures that a regulator will maintain given certain flow rates in a system.
  • Pressure-Reducing Regulator: pressure-reducing regulators control outlet pressure by balancing an adjustable spring force against the forces caused by inlet and outlet pressures. The spring force is adjusted by turning the stem/handle, which sets the desired outlet pressure. As inlet pressure decreases, the force balance changes. To compensate, outlet pressure will increase. This Supply Pressure Effect (SPE) is a function of the design and type of regulator. 
  • Seat Load Drop: the initial pressure drop experienced when a regulator starts from a no-flow state.
  • Sensing Chamber: the area just below the Sensing Element.
  • Sensing Element: component separating the spring/dome/air force and the fluid force, which responds to pressure changes in the Sensing Chamber. The stem of the Sensing Element is in constant contact with the Controlling Element, and move together as pressure changes in the Sensing Chamber.
  • Set Pressure: the desired operational outlet pressure for a regulator, set by the Loading Element, given an inlet pressure and flow requirement.
  • Single-stage Regulator: ideal for relatively small reductions in pressure, and typically do not perform well with large swings in inlet pressure and/or flow rates.
  • Supply Pressure Effect (SPE): the effect on the set pressure of a pressure-reducing regulator as a result of a change in inlet pressure, normally experienced as an increase in outlet pressure due to decrease in inlet pressure. Also referred to as dependency.
  • Two-stage (Dual-stage) Regulator: used in applications requiring constant outlet pressure even with wide variations in inlet pressure, and is comparable to two single-stage regulators connected in series. The first stage is generally factory set, and the second stage can be adjusted with the handle to achieve the required outlet pressure.

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