Nastec SUND, Инструкция по установке, использованию и техническому обслуживанию

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10. Constant pressure operation
10.1. Introduction
TheSUND can manage the running speed of the pump in such a way as to keep the pressure constant as the
water demand changes. A pressure sensor placed as close as possible to the pump is used for this purpose.
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1: Inverter; 2: Pump; 3: Check valve; 4: Pressure vessel; 5: Gate valve; 6: Gate valve; 7: Pressure sensor
10.2. The pressure vessel
In water systems equipped with inverters, the function of the pressure vessel is to compensate for losses (or
minimum water consumption) and maintain pressure when the pump is stopped, thus avoiding excessively frequent
start/stop cycles. It is of fundamental importance to correctly choose the volume and the pre-charge pressure of the
pressure vessel. Too small volumes do not allow effectively compensating the minimum water consumption or the
losses when the pump is stopped, while too high volumes make it difficult for the inverter to control the pressure.
It is generally sufficient to place a pressure vessel with a volume of about 10% of the maximum flow rate required,
considered in liters/minute.
Example
If the maximum flow rate required is 60 l/min, it is sufficient to use a 6 liter pressure vessel.
The pre-charge pressure of the pressure vessel must be approx. 80% of the operating pressure.
Example
If the set pressure in the inverter is 4 bar, the pre-charge pressure of the pressure vessel should be approx. 3.2 bar.
NOTE
The pre-charge pressure must be adjusted with the system completely unloaded.
10.3. Electrical connections
The device may be connected to linear pressure sensors with 4 - 20 mA output. The supply voltage range of the
sensor must be such as to include the 15 V DC voltage with which the device feeds the analog inputs.
The pressure sensor is connected via the terminals of the analogue input 1, i.e:
• AN1: 4-20 mA signal (-)
• +15V: 15 VDC power supply (+)
The device supports the installation of a second pressure sensor for:
• Operating at constant differential pressure (read the dedicated chapter).
• Automatic replacement of the main pressure sensor in case of failure.
• Exchange of active pressure sensor via digital input.
The secondary pressure sensor is connected via the terminals of the analogue input 2, i.e:
• AN2: 4-20 mA signal (-)
• +15V: 15 VDC power supply (+)
SUND
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