FAQ - About Fitting & Servicing Interpumps

FAQ - About Fitting an Interpump

Given below are a number of basic concepts useful for operating our pumps that provide a quick guide for their selection, installation and maintenance.

1 What is a positive-displacement piston pump?
It is a pump equipped with one or more pistons (usually 3 or 6), where the flow rate (liters or gallons per minute) is directly proportional to the rotation speed (r.p.m.).
From a technical standpoint, from 1977 on, the pumps designed and manufactured by INTERPUMP have incorporated innovative design solutions that have become the model used by manufacturers of this type of piston pump around the world. These innovations include:
  • Double seal on each plunger with low pressure intermediate chamber to keep the water seals cool and lubricated. This system also permits to recirculate any leakage from the high pressure back to pump inlet
  • Syntherized pistons of super-hard ceramic
  • Connecting rods of special alloys with low attrition coefficient, high wear resistance and high anti-seize up properties
  • Hydraulic structure designed to simplify scheduled maintenance procedures (gasket and valve replacement)
From a construction standpoint, the main components are manufactured in our factories subject to rigid controls in conformity with ISO 9001 (the company has been certified since 1993) and all finished products undergo a 100% inspection process.
2 What are the major applications for piston pumps?
Piston pumps are convenient in applications where high pressure is a basic requirement. This makes them virtually irreplaceable in certain sectors, such as:

a) High-pressure cleaning
b) Petrol and chemical industry
c) Paper mills
d) Mills
e) Reverse osmosis for water desalination
f) Construction sites
g) High pressure cutting
h) Air conditioning (cooling and humidification)
i) Tool cooling on lathes, work centers, etc.
j) Hydro-sandblasting
k) Agriculture, crop-dusting


3 What types of liquids can be pumped?
Interpump pumps have been designed and created to utilize clean, non-salt water at ambient temperature. But this does not mean that other types of liquids cannot also be pumped, as the experience of our customers shows.
Generally, for water-based solutions, the pH level must be between 4 and 11 (in any case, when dealing with levels 4 and 11, please contact our Technical Service Department).
If the water includes abrasive particles (sand, shavings, etc.) a 20-30 micron grade filter must be installed.
These pumps are prepared to pump water up to a temperature of 65°C. For these applications, the pump must be fed a min. pressure of 1 bar as read from the suction line. For some models, a kit is available for higher temperatures. In this case, please contact our Technical Service Department.
Please note that these pumps have not be designed to include the necessary requisites for pumping potentially hazardous liquids (explosive, toxic or inflammable).
4 What criteria should be used for selecting a pump?    -  What do the technical specifications in our catalogue mean?
Which pump to select from our product line normally depends on the flow rate and pressure requirements of the specific application.
Using the paired capacity/pressure criterion, it is generally possible to find a model with the right specifications. Please note that the pressure level given in the catalogue is the maximum level at which the pump may be used and, clearly, there are no limits on using the pump at lower pressures.
The indicated flow rate is obtained when the pump is running at the rated speed (r.p.m.) as flow rate is directly proportional to pump speed, it can be changed by varyng the r.p.m. accordingly.
Again, the values given in the catalog may be reduced (within a certain limit), but not increased.
Also included under pump specifications is the rating of the motor that will be connected to it. This indicates the power required from the motor when the pump is utilized at the rate specifications (pressure, flow rate, r.p.m.) given in the catalogue.
If the pump is used at lower rating, the motor power must be recalculated (see point #5).
5 How is motor power determined ?
The rating given in the catalog is that required by the pump to operate at the maximum levels given.
For coupling to electric motors, their power must be greater than or equal to that given in the catalogue.
For coupling to petrol engines, their power must be at least 30% higher than that indicated (nA curve).
In the event a specific application requires flow rate and/or pressure other than those given in the catalog, motor power can be recalculated using the formula below:
HP = absorbed power (in HP)
Q = flow rate (in l/min)
P = pressure (in bar)
385 = coefficient

To couple the pump to a petrol engine, take this result and increase the power by 30% as described above.
6 What else is needed to complete the installation?
To operate, the pump must be equipped with a safety valve or regulating valve that may also be automatic.
The safety valve is installed on the pump and adjusted (normally 10% over the maximum allowable pressure) to discharge the entire flow whenever the maximum set level is exceeded for whatever reason.
The pressure regulating valve (which may also be automatic), regulates the pressure by releasing any excess liquid delivered to maintain the installation at the correct pressure.
In some applications, for reasons of safety, both valve types (safety and regulating) may have to be installed.
In order to monitor installation pressure, a gauge with scale adequate to operating pressure must also be installed.
The INTERPUMP catalogue includes a wide range of regulating, automatic and safety valves, as well as a number of other accessories to be used for high pressure cleaning (lances, guns, fixed and rotating nozzle heads, etc.). Other accessores (couplings, flanges, pulleys and gear reducers) have been developed to facilitate the most common types of pump/motor coupling.


7 How is the pump installed?
For correct pump installation, follow these instructions:
Hydraulic connections:
  • Using appropriate piping, connect the pump inlet and outlet as shown: 
  • The diameter of the inlet pipe must be greater than or equal to the diameter of the pump inlet port and must be straight and as short as possible (a few meters long, at most). It must either incline up or down towards the pump and connections that could create air pockets must be avoided. Avoid installing components that could case restrictions on the inlet line. Even if the water is clean, a filter with a filtering level of 350 micron or less must be installed on the inlet line and it must have a greater capacity than the flow rate of the pump filter must be cleaned periodically
  • All pipes hoses and accessories connected to the pump outlet must be adequate for pressure levels greater than or equal to the pressure set for the safety valve and/or regulating valve
  • The pump may be fed under pressure directly from the water mains with a maximum pressure of 10 bar. If the pump intake is from a tank, it is preferable that the water level be above the pump or at the same level. If the water is sucked up from below the pump, the difference in level must not be greater than 3m for pumps up to 1750 revs/min and 1m for those at a faster speed and, in this case, the water must be at ambient temperature. Problems with priming, vibrations or excess noise are all symptoms of poor water supply and could cause serious damage to the pump. If any of these symptoms should appear, we suggest that the pump be stopped immediately and the water supply connection checked
Mechanical installation:
  • In the event INTERPUMP flanges and couplings are used (available for a range of models), correct connections is guaranteed by the accuracy in the machining of INTERPUMP components and the same is also true of INTERPUMP gear reducers. With this type of coupling, take care to fix the motor to the base of the unit (using rails or silent blocks if needed), leaving the pump free
  • If the pump is driven with belts and pulleys, pay special attention to pulley alignment and belt tension (to do this, the pump must be assembled on a special belt-tightener slide with adjusting screws). Please note that if the belts are too tight, the oil could overheat and reduce bearing life. For more information on pulley and belt size, please refer to the technical specifications supplied by the manufacturer of the transmission belts
  • Direct coupling using a flexible joint without flange is more difficult. In this case, both the pump and motor are attached to the unit base and, before connecting pump to motor, the two shafts must be perfectly aligned, if necessary using spacers under the feet of the pump or motor. The purpose of this is to avoid pressure on the pump and motor bearings. If the pump has been coupled using the joint or belts and pulleys, all exposed moving parts must be protected with joint- or belt-guards

8 What are the most common problems encountered during operation?

Pump is running but does not reach the pre-set pressure
Pump is sucking in air Check inlet ducts and make sure they are air-tight
Valves are worn Check and replace
Regulating valve seats worn Check and replace
Nozzle inadequate or worn Check and replace
Seals worn Check and replace
Pump not sucking
Pump is sucking in air Check inlet ducts and make sure they are air-tight
Suction level too low Check inlet water level
Inlet valves dirty Disassemble and clean the inlet valves or connect the pump inlet to the water mains and pump for a few minutes
Irregular pressure oscillation
Inlet and/or outlet valves worn Check and replace
Foreign matter present in the valves jeopardizing their functioning Check and clean valves
Pump is sucking in air Check inlet ducts and make sure they are air-tight
Water seals worn Check and/or replace seals
Drop in pressure
Nozzle worn Change nozzle
Inlet and/or outlet valves worn Check and/or replace valves
Check and clean valves
Foreign matter present in the valves jeopardizing their functioning Check and/or replace the regulating valve seat
Regulating valve seat worn Replace
Water seals worn Replace seals
In case of belt drive, belts are slack or worn Replace belts or adjust tension
Excessive noise
Pump not being fed correctly Check that the suction level is not too low or that the suction pipes are not blocked (e.g., filter clogged)
Pump is sucking in air Check inlet ducts and make sure they are air-tight
Inlet and/or outlet valve springs damaged or broken Replace valve springs
Foreign matter in inlet/outlet valves Check and clean the inlet/outlet valves
Bearings worn Replace bearings
Fluid temperature too high Reduce the temperature of the pumped fluid
Water traces in oil
Excessive leaks caused by totally worn water seals Replace seals
High humidity rate in air Change oil twice as often as recommended
Water seeping from drains between head and crankase
Water seals worn Replace seals
Piston damaged Replace piston
O-ring on piston bolt worn Replace O-ring
Oil seeping from drains between head and crankase
Oil seals worn Replace oil seals
Frequent or premature wear of water selas
Pistons damaged or scratched Replace pistons
Abrasive matter in water Install the proper filter on the inlet side
Water temperature too high Check temperature of inlet water
Pump running dry Avoid running pump without water
Operates for long periods in by-pass Limit by-pass mode running to no more than 5 min.
Excessive vibrations at outlet hose/pipe
Pulsation dampener drained (where present) Check pressure in pulsation dampener
Valves worn or dirty Check and replace
Pump is sucking in air Check inlet ducts and make sure they are air-tight
Water seals worn Replace water seals

eep the pump in good working orde

9 What maintenance procedures are required to keep the pump in good working order?
INTERPUMP pumps are delivered ready with their first oil filling and transport plug (red) to prevent oil leakage during shipping. Oil dip-stick with level gauge and breather hole (black/yellow) are supplied separately. Before starting up the pump, replace the transport plug with the dip-stick.
The first oil must be changed after the first 50 hours of pump operation, while successive changes are required every 500 hours.
We recommend the use of INTERPUMP X.9.9. (SAE 20/30) or equivalent oil (included with each pump is an instruction manual listing compatible oils).
Between oil changes, periodically check the oil level in the clear gauge or using the dip-stick, and top-up if necessary.
During scheduled checks, also check that water has not seeped into the oil (if it has, the oil will be whitish in color).
Seepage may be caused by excessive seal leaks (poor maintenance) or condensation build-up in surroundings that are very humid or subject to wide temperature swings.
Other components subject to wear that must be periodically checked and replaced are the gasket seals and suction and delivery valves.
Seals wear can be noticed by a drop in pump pressure or formation of drops under the pump where the head is connected to the crankase.
If this happens, the entire seal set must be replaced as soon as possible to avoid water seeping into the crankase and damaging mechanical parts.
To replace the seal, use the special tool kit or those found in our tool case; always use original spare parts.
Wear can be noticed by a drop or variation in pressure, and often machine vibrations of inlet/outlet valve.
If the pump is to remain inactive for an extended period of time, it is a good idea to drain it completely. To do this, disconnect the inlet and outlet pipes and run the pump empty for a few seconds (10 sec. max.). This precaution is absolutely indispensable if the pump is to remain at a temperature below 0°C, even for a short period of time.


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At the foot of the pump page under “Related Products” – you will see the popular Interpump service Kits & Interpump Spare Parts relating to that pump.


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