Control
- Adjustable ejectors (e.g. HDV-E30) have a bipolar servomotor by means of which the position of a throttle element and thus the cross-sectional area of the nozzle in the ejector can be changed.
- To control the valve, the following is needed:
- an analogue control signal (0..10 V) from the superior controller (independent of the manufacturer)
- the control device SVD1A1
- the activation of the bipolar servomotor (via the control device)
Control device SVD1A1
Connect cables to the ejector only with a seal (included in delivery). Tightening torque for the connector: 0,5 Nm.
For any work performed on the electrical system: Observe the protection objectives of the EU Low Voltage Directive , EN60204-1, the IEC60364 series of safety standards and national safety regulations.
Malfunctions due to electromagnetic interference!
When connecting ejectors with a cable length > 5 m, use shielded connection cables.
Connect the shield to terminal 35 and the earth to terminal 34.
The SVD1A1 is inactive when the combination 0/0 is set on the rotary switches!
Setting the ejector group and ejector type:
- Set ejector group "8" (left-hand rotary switch) and ejector type "0" or "1" (right-hand rotary switch) on the rotary switches of the control device (see figure below).
Ejectorgroup "8" | HDV-E23/HDV-E30 |
Type "0" | 100% of the Kv value |
Type "1" | 100% of the Kv value |
Cable lengths and cross sections:
- < 5 m -> 0.5 mm2
- 5-30 m -> 0.5 mm2 shielded
- 30-50 m -> 0.75 mm2 shielded
Settings for emergency operation / in case of voltage supply interruption:
- The ejector position (open or closed) is preset directly on the switch for the safe valve position (safe pos.) of the SVD1A1 (see figure above, switch to the right of the rotary switches).
- SVD1A1 has an integrated emergency closing function for emergency operation / in case of voltage supply interruption.
Control characteristic
In the applications described in this Technical Information, the ejector controls the optimum high pressure via a control characteristic (depending on the manufacturer of the superior controller). For control, the measured high pressure for the temperature at the gas cooler outlet, which is also measured, is compared with the target high pressure using the control characteristic.
- Depending on the control deviation between the measured high pressure and the target high pressure, an analogue control signal is output by the superior controller. The control device is used to activate the bipolar servomotor and thus change the cross-sectional area of the nozzle.
- The mass flow ratio (entrainment) is influenced by controlling the cross-sectional area of the nozzle and thus the high pressure. When using the ejector as a low lift / liquid ejector, this dependency must be taken into account when planning and designing the system.
- The height of the pressure lift may only be selected such that no stall effect occurs in the ejector even at low high pressure and motive mass flow.
- For some ejector applications, a distinction can be made between different operating conditions, for example with an open or closed suction line for the ejector.
- One criterion for activating the various operating conditions is the gas cooler outlet temperature or the inlet temperature of the motive mass flow into the ejector. However, the gas cooler outlet temperature alone does not provide information on the load requirements at the cooling points.
- Depending on the manufacturer and type of the superior controller, further criteria are taken into account, for example opening degree of the flash gas bypass valve, opening degree of the high-pressure control valve, operation feedback of the compressors, superheat and alarm messages.
