Clean Compressed Air Brochure - Norgren - #12

NORGBEW

Pilot operated regulators are ihose which do not have a direct mechanical means of adjusting the outlet pressure This eliminates leverage problems in achieving high (16 bar plus) pressures in large pipe size units. The outlet pressure Is controlled by means of an air pressure signal (Figure 23) which Is normally produced by a preci­sion regulator. This allows tor example a pilot operated regulator to be remotely situated In the large distribution mains normally- in a building's roof, but be adjusted to give the desired output pressure from shop door level. For the majority of pilot operated applications it is best to take the system or outlet pressure reading from the pilot operated (often called aslaveor main) regulator Itself or the distribution system as the pilot regulator's outlet pressure is generally not the same.

Pilot operated regulators also give better performance by eliminating the control spring and usually have a large diaphragm area compared to valve area which also Improves the accuracy ot pressure control In response to small pressure changes.

Another level ot control accuracy ;an to relieved by employing a feedback .i. ■ !■ i -i■ 11 Ttiis device senses the outlet pressure in the system and a piped connec­tion feeds this signal back to the pilot

regulator which compares it to the desired outlet signal and 'compensates' by increasing

high. This type of control is usually employed where a large steady air flow to a continuous process Is required.

Precision regulators (or controllers) are normally used for instrumentation applications where exact repeatability and freedom from outlet pressure setting drift over short or long term operation is neces­sary. These regulators normally have a sma'l outlet flow range, but exhibit superior flow and regulation characteristics. Their ability to achieve the ideal of these characteristics over flow and pressure ranges is reflected in their si a; and price.

Generally most precision regulators employ a special arrangement to allow a constant bleed of air to escape to atmos­phere. Although this Isacostto system as a whole, being a loss of air, It Is the price which must be paid In order to achieve the very fast response to the applications demands needed to keep the system pressure as constant as possible. The best types of precision regulators also employ an integral pilot operation, producing era;! ve:y two diaphragms and valves, one small and sensitive the other a slave to ensure that the

Figure 24.

NOFGREN MICFOTFOL PRECISION REGULATOR

overall performance meets the requi rements of the particular application.

Another feature of precision regula­tors Is their relief capacity and some have the ability to relieve up to 80/90% of their recommended regulated flow for specialist application such as tensioning belts, paper rolling and balancing. (Figure 24).

Special purpose regulators can cover a whole range of specific demands Including meeting exact environmental requirement':, with .■■ ■ ■ i na ia navng high relief flows, plunger operation in place of handwheels etc. They can be derivatives of any of the other types of regulators with application specillc additions.

Ensure the regulator chosen exactly tits the performance requirements of the application, ft regulator which controls the pressure to a distribution main Is usually of the general purpose type or for large volume/How applications pilot operated.

Decide it the performance requi re­ments need a standard or precision relator Then decide if the Bow capacity of the regulator is suitable for the pipe size needs [see figure 38) and check with the regulators (low characteristics. Figure 25 shows flow ratings ol Norgren General Purpose Regulators. II there Is no variation in the Inlet pressure to an application then the regulation characteristic of the regulator Is unimportant but the flow characteristic will be II the Inlet pressure Is exposed to ■.■■a'ialio^,,5 hen the regulation characteristics

Figure 23.

A TYPICAL PILOT OPERAIS) REGULATOR INSTALLATION.