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Series 74 Valve Positioners

Brand: Siemens Aktiengesellschaft

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The Model Series 74 Valve Positioners are universal positioners that provide versatility, dynamic performance, and high positioning accuracy.

They use the piston or diaphragm in a pneumatic actuator to position a valve to what is required by a control instrument and hold that position, regardless of the presence of forces that change valve position.

As such, supply pressure variations have little or no effect on the positioner output, which eliminates the need for a supply pressure regulator.

These valve positioners are two-stage, pilot-operated instruments.

The pilot circuit activates dual-output boosters, which perform opposite actions: when one booster is supplying air, the other is exhausting air.

This “push-pull” action applies to a full differential: supply pressure to atmosphere, across the actuator to drive the valve to the position required by the control instrument signal.

Model 74 Valve Positioners can also be used for single- acting service on a spring-loaded actuator.

In this case, one of the pilot-booster connections is plugged.
Features
  • Double-acting or single-acting service accommodates installation in a variety of environments
  • Field reversibility reduces downtime and simplifies maintenance
  • Choice of continuously adjustable standard stroke ranging from 1/4" to 48" and continuous span and zero adjustability within range spring limits provide application versatility
  • Extra high capacity pilots ensure maximum frequency response and optimum stroking speeds for all actuator sizes
  • Negative feedback pilot circuit allows the positioner to operate with a push-pull gain of more than 900:1 - using100 psig supply - with no sacrifice in stability
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The Model Series 74 Valve Positioners are universal positioners that provide versatility, dynamic performance, and high positioning accuracy.

They use the piston or diaphragm in a pneumatic actuator to position a valve to what is required by a control instrument and hold that position, regardless of the presence of forces that change valve position.

As such, supply pressure variations have little or no effect on the positioner output, which eliminates the need for a supply pressure regulator.

These valve positioners are two-stage, pilot-operated instruments.

The pilot circuit activates dual-output boosters, which perform opposite actions: when one booster is supplying air, the other is exhausting air.

This “push-pull” action applies to a full differential: supply pressure to atmosphere, across the actuator to drive the valve to the position required by the control instrument signal.

Model 74 Valve Positioners can also be used for single- acting service on a spring-loaded actuator.

In this case, one of the pilot-booster connections is plugged.
Features
  • Double-acting or single-acting service accommodates installation in a variety of environments
  • Field reversibility reduces downtime and simplifies maintenance
  • Choice of continuously adjustable standard stroke ranging from 1/4" to 48" and continuous span and zero adjustability within range spring limits provide application versatility
  • Extra high capacity pilots ensure maximum frequency response and optimum stroking speeds for all actuator sizes
  • Negative feedback pilot circuit allows the positioner to operate with a push-pull gain of more than 900:1 - using100 psig supply - with no sacrifice in stability

Specifications

Input Ranges

  • 3-15 psig
  • 3-9 psig
  • 3-27 psig
  • 0-15 psig
  • 0-30 psig
  • Split ranges within these basic ranges

Valve-Stroke Ranges

  • 1/4" minimum
  • 48" maximum

Supply Pressure

  • 3 psig above full actuator pressure minimum
  • 150 psig maximum

Air Consumption

  • 0.2 scfm - Imbalanced condition with 20 psig supply

Overload Protection

  • 150 psig at any connection

Response Level

  • Output is sensitive to control signal changes as small as 0.1 % of full range

Ambient Temperature Range

  • -40° to 180° F
  • -40° to 82° C

Materials of Construction

  • Aluminum
  • Brass
  • Stainless Steel
  • Buna-N

Linearity

  • ± 1.5 % F.S.

Input Range

  • 3-9 psig
  • 9-15 psig range requires a suppression spring
  • 3-15 psig

Actuator Motion

  • 90° Rotation