Borehole Pumps

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).

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.

How do I connect a single phase electric submersible motor? Or a three-phase?

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 should the connection between the cables coming out of the submersible motor and the power cables be performed?

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.

Sewage Pumps

Are there any particular instructions for ATEX version electric pumps (explosion proof)?

  1. Do not work on cable glands or open the motor casing; these works are reserved to Caprari authorised workshops.
  2. The operating characteristics of these machines must comply with the characteristics specified in the nameplate and in the attached EX certificate.
  3. Minimum head is at the top of the electric motor for S1 machines and on pump casing for electric pumps intended for intermittent duty S3
  4. The temperature sensors must be connected to electric pump control equipment. The temperature sensor tripping must cut the electric pump power supply. Reset must not be automatic, but should be possible only after inspection by qualified staff.
  5. No change to the machines or replacement of parts of the electric motors is allowed. It is allowed to only replace wet end parts with identical genuine parts (same part number or same code on the part) in case of normal wear and tear. Any service other than ordinary maintenance can only be carried out by Caprari S.p.A.
  6. The optional use of the conductivity sensor installed in the motor casing is conditioned on the use of a control device installed in the control panel and compliant with potentially explosive environment requirements.”
  7. Activate all possible measures to prevent the following malfunctions as they could cause and trigger an explosion:
    – operation with no fluid in the pump or zero flow rate: arrange suitable direct control devices with manual reset on the control panel
    – failure of pump shaft bearings: in case of an increase in vibration and/or noise in operation, stop the pump and send it to a Caprari authorised workshop
  8. Operation with inverter/converter: use of this kind of electronic equipment for control and adjustment must be carefully designed to make sure it does not generate any electromagnetic noise or induced current that would reduce the safety standard required by the ATEX class of the area where equipment is operating. The following conditions must always be complied with
    – mandatory use of inverters by Danfoss, series VLT FC202 or more recent Danfoss models having enhanced performance and characteristics; use of corresponding models from other brands must be authorised by Caprari S.p.A.;
    – mandatory setting for the internal switching frequency of the inverter at maximum 4kHz or at the lowest frequency allowed by the inverter;
    – mandatory installation on the inverter of suitable filters for reducing the [dv/dt], in-between inverter and motor;
    – mandatory use of the inverter only within 35-60 Hz modulation range.
  9. Max. standard ambient temperature is 40°C; on request, after Caprari S.p.A. checks, a maximum ambient temperature up to 60°C may be accepted, and this temperature will be indicated on electric pump nameplate.

What checks can be done if current imbalances are detected on the three phases of the motor?

Absorption differences on the three motor phases (greater if detected without load) are not always due to a construction defect since even the supply can be unbalanced.
If a high imbalance is detected (under optimal voltage conditions) also check absorption on the other two motor/mains connection combinations; (to maintain the same rotation direction, proceed according to the diagram):
Optimal connection is when the difference between absorptions is the least.
However, if the highest absorption is always detected on the same phase of the line the main cause of imbalance is due to the supply.
N.B.: Max. permissible imbalance on absorbed current: 5%.

What is the maximum temperature of the pumped liquid?

The maximum temperature of the pumped liquid is 40° C.

How does a higher density of liquid affect motor power?

A density higher than 1 Kg/dm 3 and/or viscosity higher than 1 mm 2 /s inevitably involves an increase of power absorbed by the motor, with subsequent overheating and burning of the winding if there are no thermal protectors.

Possible suggestions:
Use a motor of higher power: the percentage increase in motor power must be at least equal to the density percentage.

Use of an impeller of smaller diameter than standard.

To avoid possible obstructions and clogging, it is advisable to check that the velocity of the liquid in the delivery piping stays above 0.8-1 m/s. In the presence of sand, at least 1.6 m/s is required in the horizontal piping and 2.5 m/s in the vertical.

To ensure that a submersible pump functions correctly, what is the minimum level of fluid allowed?

The minimum level of fluid required for a submersible electric pump immersed in that fluid differs, depending on the type of service (A1=continuous service/S3=intermittent service). This is why it is pre-engineered for installation of a cooling casing if required.

INSTALLATION WITHOUT THE COOLING CASING
S1 operation: the motor must be completely immersed in the pumped fluid.
S3 operation: the fluid can reach the base of the motor. However, the electric pump can only operate in these conditions for a certain period, alternated by the period at a standstill required by the motor.

OPERATION WITH THE COOLING CASING 
The motor can operate completely uncovered by the fluid in the S1 service mode.

What is cavitation?

The phenomenon of cavitation is due to the formation and subsequent implosion of vapour bubbles forming inside the impeller blades due to an internal pressure lower than the vapour pressure of the pumped liquid at a given temperature.
With waste water electric pumps cavitation can occur for the following reasons:

  • Suction pipe too long (only in the case of installations in dry chamber)
  • Intake of small quantities of air bubbles due to the creation of vortices caused by the dynamic level lower than m…
  • If the effective work duty point goes outside the normal electric pump utilization field
  • Water based liquids with temperatures above 80°C.

N.B.: Cavitation can cause the following malfunctions:

  • Changes in hydraulic performance
  • Excessive noise (rattling)
  • Violent vibrations with possible failure of seals, bearings and the shaft

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 °

<= 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 a Caprari K Series submersible electric pump be installed with an automatic coupling support (duck foot pedestal) by another producer?

The possibility of coupling using adapters with the main coupling supports in production is provided for.

How can I establish the correct direction of rotation of the electric pump?

The terminals of the power cable are marked with the IEC international codes. Their correct connection to the L1(u), L2(v), L3(w) line ensures that the electric pump turns in the right direction. The arrow on the casting on the top part of the motor indicates the correct direction of rotation, i.e. clockwise viewed from above. If the installed unit is visible when started, it will be subjected to kick-back in the anti-clockwise direction.

If it is impossible to directly check the direction of rotation (e.g.: when the electric pump is already installed), it is advisable to compare the hydraulic performance parameters and the motor’s electric power input with the electric pump’s data plate values.

Switch two of the phases with each other to invert the sense of rotation.

How is the conductivity sensor connected to the electrical panel?

If the Caprari electrical panel, already arranged for sensor connection, is not available, it is possible to ask the sales network for the appropriate CLM/3S-24V motor oil chamber water detection sensors.

What is the purpose of the "S" conductivity sensor in K Series models?

The conductivity sensor is inserted in the oil chamber and detects any water infiltration in the chamber from the mechanical seal. If the electrical panel has a detection device just connect the terminal with the “S” symbol and a branch of the yellow/green earth wire.

The conductivity detection device is used to activate an alarm circuit in the event water is detected in the oil.

The alarm can be either visual or audible. For explosion proof motors the devices used must be intrinsically safe and compatible with the zone classification in which they are in use.

When should the oil in the electric pump oil chamber be changed?

In normal operating conditions the oil must be changed every 10000/15000 hours.

Use SAE 10W oil. If there is water in the oil, check the condition of the pump side mechanical seal and replace it if necessary.

How must K Series heat sensors be connected (T1 and T2)?

The heat sensor terminals, marked with the symbols T1 and T2, must be connected in series to the electric pump command remote control switch coil (see the general cable wiring diagram in the operator’s manual). The heat sensors are normally closed bimetal switches embedded in the motor windings. When the temperature of 132°C is exceeded they open, breaking the remote control switch coil feed circuit and causing the electric pump to stop.

The coil is excited again when the sensors have cooled (114°C). The sensors can be connected with a max. of 250V. A power supply of 24V – 1.5°? is recommended.

For pumps with explosion proof motors (type ..X.. ) the connection of the temperature probes is compulsory. Failure to do so will invalidate the warranty.

Can K Series submersible electric pumps be used to pump drinking water?

All the paints used have certification of suitability for contact with drinking water.
Upon request the pump oil chamber, normally filled with mineral oil – viscosity SAE 10W, can be filled with dielectric oil approved by the Food and Drug Administration (U.S.A.) and suitable for contact with food substances.

Vertical pumps

What is submergence?

Submergence “S” is the minimum immersion depth required by the pump to prevent the formation of vortexes. It varies according to the size of the pump and the rotation speed. As an indication, it is 2,5 times the diameter of the hydraulic part but, therefore, must be adapted to the NPSH conditions required by the pump.

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