Why must one or more non-return valves be used in installations of submersible electric pumps?
Non-return valves are used to maintain the pressure in the system when the pump stops. They also prevent possible problems of water hammering, counter-thrust and counter-rotation:
Water hammer: If the valve nearest the pump is placed at more than 10 metres from the static level of the water, or the lower valve leaks whereas the upper one holds, a pressure drop could be created inside the piping. At the next pump start, the water displacement at high speed fills the vacuum and beats against the upper valve and the water in the delivery pipe causing a water shock.
Counter-thrust: Without a non-return valve, or with a faulty non-return valve, in the first electric pump start phase operation could occur without water column conditions in the delivery pipe). This causes an axial thrust on the impellers and pump shaft towards the delivery. This axial thrust is transmitted, through the electric motor/hydraulic part coupling, directly to the motor creating a counter-thrust operating condition. Repeated counter-thrusts can cause early breakdown of the motor and the hydraulic part.
Counter-rotation: Without a non-return valve, or with a faulty non-return valve, the water contained in the rise pipe and in the rest of the system would start to flow in the opposite direction on pump stop, causing rotation in the opposite direction to that of normal operation. If the electric pump is restarted during this phase a high twist force would be generated on the motor pump assembly. Another effect could be excessive wear of the thrust bearing due to the shaft rotation not being fast enough to assure the presence of a film of adequate thickness between the thrust block and the motor thrust bearing blocks.
Can Caprari products be used for pumping drinking water?
All the paints used in the hydraulic parts have certification of suitability for contact with drinking water. M…4-MH…4-MK…4… type submersible motors are supplied ready for use and filled with oil (for lubrication and cooling), approved by the Food and Drug Administration (U.S.A.). M…6…M…12… type motors are supplied filled with a mixture of 70% clean fresh water and 30% DowFrosth 1.2.3.type propylene glycol from Dow Chemical, classifiable as non-hazardous according to the criteria established by the EEC. At the time of installation the mixture can be replaced with clean, filtered fresh water, but never distilled water (see the Operator's Manual, par. 5.1 "Preliminary checks" for the relevant procedure).
Even the power cable supplied by Caprari (EPDM – Blue type) has WRAS certification for use with drinking water.
The electric pump does not provide the performance declared in the documentation. What test can be done in order to know if the low performance is due to the electric pump or the installation?
By closing the electric pump delivery gate valve, the pressure generated at no flow condition can be identified (Q=0) using a pressure gauge. The manometric (gauge) head, added to the height between the dynamic liquid level and the gauge point, should coincide with the value indicated on the electric pump performance curve at Q=0.
What is the max. water temperature for the standard submersible motors?
The submersible motors with standard winding are not suitable for pumping water at temperatures above 25°-30° C (see the "Motors table" chap. 10 of the operator's manual supplied with the electric pump). For higher temperatures request motors with special winding for high temperature. Contact the main office or the sales network.
What size of capacitor must the 4” single-phase motors have? Is it a permanently inserted capacitor?
All our 4” single-phase electric motors are equipped with permanent capacitor, installed in the starter box.
What filling liquid is used in the 4" submersible motors?
Caprari 4” submersible electric motors are all oil filled. The dielectric oil used is MARCOL 82 (ESSO) approved by the Food and Drugs Administration and suitable in case of contact with substances for food use (drinking water).
Can Caprari’s submersed electric pumps be used with electronic starting systems (Soft-Starter/Inverter)? If they can, are there any specific instructions to comply with?
Standard submersed motors can also be used with multi-frequency starters.
The use and maintenance manual of the electric pump gives instructions that must be complied with if an Inverter or Soft-starter is used.
General instructions for use of the INVERTER:
- the minimum frequency must not be less than 70% of the rated value during the starting phase and/or use, with the voltage/frequency ratio maintained at a constant level.
A filter that ensures the following voltage gradient must be installed between the inverter and motor:
- (dV / dt) ≤ 750 V/µs for motors in oil
- (dV / dt) ≤ 500 V/µs for motors in water and propylene glycol with standard winding and well tmax C ° ≤ 25 °C
- (dV / dt) ≤ 650 V/µs for motors in water and propylene glycol with special winding and well tmax C ° ≤ 35 °C
<= 1.5% harmonic voltage content.
<= 4 % harmonic current content.
Conditions to be complied with regardless of the length of the power cables.
General instructions for use of the SOFT-STARTER:
The SOFT-STARTER device must be the voltage ramp and not the current ramp type.
- always make sure that the soft-starter is cut out once the starting phase of the assembly has terminated.
If an installation with a soft-starter or inverter starting system functions in a faulty way, check the operation of the electric pump assembly by connecting it straight to the electricity main (or to another device).
Can Caprari's submersed electric pumps be installed in horizontal/oblique positions?
Caprari’s 4”-22” submersed electric pumps can be used in the horizontal/oblique positions, but the Caprari headquarters or sales network must be consulted prior to purchase. These machines must be modified in certain ways to allow them to function in these positions.
Come devo collegare un motore elettrico sommerso monofase? E trifase?
Single-phase and three-phase motors must be connected as shown in the following diagrams and in compliance with the indications given on the motor’s data plate and in the use and maintenance manual.
How must the joint between the cables leaving the submersible motor and the feed cables be executed?
Join the feed and earth cables as described in detail in the instructions provided with the jointing equipment, and then measure the connection isolation resistance: min. value with test voltage 500 Vdc in air 5M Omega, in water 2M Omega. The connection must resist the max. pressure it is subjected to, e.g. that exerted by the static level of the water in the well, and the thermal variation due to the duty cycle. N.B.: a poorly executed connection can easily cause damage to the motor and/or power cable.
At what depth must a submersible electric pump be installed in a well?
In order to guarantee correct submersible motor operation, it is necessary to make sure that the motor is at least 2/3 metres above the bottom of the well.
The well's inlet filters must also always be below the position occupied by the motor, in order to guarantee correct cooling.