Actuator operation

The electro thermal actuators STA.. and STP.. feature silent operation and are maintenance-free. When the control signal is applied to the actuator, the temperature of the heating element rises, which causes the solid expansion medium to expand. It transfers its stroke directly to the installed valve.

The valve starts to open after preheating for approximately 2 minutes if the heating element is switched on in a cold state (room temperature) and achieves the maximum stroke after another ca. 3 min (AC 230 V) or 2 min (AC/DC 24 V). The expansion element cools down when switched off and the actuator spring closes the valve (NC variants).

Actuator variants

NC (Normally Closed)

NO (Normally Open)

Actuators

STA..

STP..

De-energized

  • Valve stem is fully extended.
  • Valve (NO) is closed.
  • Valve stem is retracted.
  • Valve (NC) sppring closes the valve.

Action at startup

  • Valve stem retracts.
  • Valve (NO) spring opens the valve.
  • Actuator stem is fully extended.
  • The valve (NC) spring opens the valve.

Parallel operation of multiple actuators

Possible for all actuators, limited by the output power of the controller.

Not suitable in combination with PDM / TPI.

Valve

Examples:

  • Zone valves (V..I46..)
  • Radiator valves (V..N..)
  • Small valves (VD1..CLC)
  • Radiator PICV (VPD..-135, VPE..-135, VPU..-135, VQ..46.., VP..46..: DN 10, 15, 20, 25, 32)

Example:

  • Small valves (V..P47..)

State without Actuator

  • Valve (NO) is open wihtout actuator.
  • Valve stem is fully extended.
  • Valve (NC) is closed without actuator.
  • Valve stem is fully extended.

Some controllers control the valve actuators with PDM signals. For optimum control, the ambient temperature of the actuator must be < 40 °C.

First open function

The NC version has a first open function (activated as part of the delivery). The first open function allows low-force assembly of the actuator and is used to flush the plant prior to commissioning. The first open function automatically unlocks once power is connected (for more than 6 min.) during commissioning.

With some valve-actuator combinations with STA..65, the first open function can be triggered during installation and is then no longer active. This affects the following valves:

  • VPP46.. 2.5mm stroke / VPI46.. 2.5mm stroke
  • VVI46../2, VXI46../2
  • VXP47.., VMP47.., VVP47..

Definition NC/NO

NC versions are closed when deenergized:

The valve (NO) is closed when idle after the actuator (NC) is assembled. The actuator stem retracts and the valve opens as soon as the actuator is connected to power.

Valve state with deenergized actuator: Closed.

NO versions open when deenergized:

The valve (NO) is open when idle after the actuator (NC) is assembled. The actuator stem fully extends and the valve closes as soon as the actuator is connected to power.

Valve state with deenergized actuator: Open.

The valve is closed in a deenergized state for most valve applications featuring thermal actuators.

Actuators with the opposite control action are used when the reserved function is required: The valve is open in a deenergized state.

⇒ NO function: STA.. + NC valve / STP.. + NO valve

Response on a deenergized actuator

Valve

Type

STA..

STP..

Radiator valves

VDN.., VEN.., VUN..

Closed

Open 1), 2)

Small valves

VD1..CLC..

Closed

Open 1), 2)

VVP47.., VPI47.., VMP47..

A ↔ AB open 1), 2)

A ↔ AB closed

Zone valves

VVI46.., VXI46..

AB ↔ A closed

AB ↔ A open 1), 2)

PICV

VPD..-135, VPE..-135, VPU..-135

Closed

Open 1), 2)

VPP46.10..

VPP46.., VPI46..: DN 15, 20, 25, 32

VQP46.., VQI46..

1)

Controller must support NO valve-actuator combinations.

2)

Combination not recommend since is does not make sense from an energy viewpoint outside demand periods.

Positioning times, opening / closing

2-position

6.5 mm

4 mm

NC
STA

  • The valve (NC) is opened uniformly by stem movement when switched on and preheated.
  • The valve (NC) is closed uniformly by the closing force of the compression spring by switching off the voltage and after the hold-up time has elapsed.
  • The closing force of the compression spring is matched to the closing force of the valves and keeps the valve (NC) closed when the valve is deenergized.

NO
STP

  • The valve (NO) is opened uniformly by stem movement when switched on and preheated.
  • The valve (NO) is opened uniformly by the closing force of the compression spring by switching off the voltage and after the hold-up time has elapses.

1

Stroke

4

Hold-up time (ca. 2 min at 25° C)

2

Voltage

5

Time

I

on

6

Switch-on time

0

off

7

Voltage switched on

3

Preheating time (ca. 2 min at 25° C)

8

Switch off time

Some room controllers control thermal actuators with PDM/TPI signals. This increases response time. The ambient temperature of the actuator must be < 40°C for optimum control.

Control of modulating drives

6.5 mm, with valve stroke detection

4 mm, with valve stroke detection

1

Actuator travel (mm)

5

Stem fully extended (NO actuator)

2

Valve adapter edge

6

Valve stroke

3

Voltage range 0…10V

7

Stem fully retracted (NC actuator)

4

Overstroke range 1)

1)

The overstroke (~ 0.5 mm) ensures reliable closing of the valve/actuator combination over the entire service life of the electrothermal actuator. The position indicator protrudes slightly as a consequence.

Electronic position feedback

STA162.65L10; STP162.65L10

6.5 mm, with position feedback

Voltage

< 0.5 V

No function or no contact

1 – 9 V

Voltage output is proportional to valve stroke

1 V: Stem fully extended

9 V: Stem fully retracted

Applies to NC and NO actuators

> 9.5 V

Internal error

Voltage output while initializing the actuator: 5V

1

Actuator travel (mm)

4

Overstroke range 1)

2

Valve adapter edge

5

Valve stroke

3

Positioning signal 1...9 V

1)

The overstroke (~ 0.5 mm) ensures reliable closing of the valve/actuator combination over the entire service life of the electrothermal actuator. The position indicator protrudes slightly as a consequence.

Valve stroke detection

STA161.40L10

STA161.65L10

STA162.65L10

STP161.40L10

STP161.65L10

STP162.65L10

The actuator determines the valve stroke and automatically adjusts the active control voltage range accordingly.
This enables the valve to be actuated even more precisely and prevents the drive from running empty. The full voltage stroke of the controller is used for flow control.

 

NC variant:

The actuator is opened without power by the First-Open function when delivered. During initial commissioning, the First-Open function unlocks automatically by applying the operating voltage and detects the valve stroke. The entire initialization process takes approximately 33 minutes. The First-Open function unlocks after approximately 6 minutes and detects the valve stroke after another 27 minutes. The actuator is then fully operational.

 

NO variant:

During initial commissioning, the valve stroke is detected by applying the operating voltage. The entire initialization process takes approximately 33 minutes. The actuator is then fully operational.

 

Example: STA161.65L10:

 

 

1

Actuator travel (mm)

3

Overstroke range 1)

2

Control voltage range 0…10 V

4

Valve stroke

1)

The overstroke (~ 0.5 mm) ensures reliable closing of the valve/actuator combination over the entire service life of the electrothermal actuator. The position indicator protrudes slightly as a consequence.

The actuator automatically adapts to new valve positions if the actuator is mounted on the valve after commissioning or the valve is replaced. The learning process takes place in steps and lasts up to 24 hours, depending on environmental influences such as ambient temperature and valve type. The new positioning is permanently saved after the process is completed.

 

Position indicator

The movement and position of the actuator valve is indicated by the position indicator (1).

Actuator version NC (STA..) extends the position indicator and retracts the actuator stem when the actuator is energized.

Actuator version NO (STP..) extends the position indicator and the actuator stem when the actuator is energized.

With modulating actuators, types STP162.. and STP161.., the position indicator remains retracted throughout the entire regular stroke range. The indicator extends and indicates the position only after an overstroke.