Frequently Asked Questions 

Frequently asked questions

Below are some of the most frequently asked questions regarding Interpump pumps, their selection and installation. We trust these will answer some of your questions but don't hesitate to contact us regarding any further assistance or advice we can provide.

1. What is a positive displacement piston pump?
A positive displacement piston pump 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 1977 the pumps designed and manufactured by Interpump have incorporated innovative design solutions that have become models for manufacturers of these types of pumps around the world. These innovations include:

  • Double seals on each plunger with a low pressure intermediate chamber to keep the water seals cool and lubricated, this system also permits any leakage to recirculate back to the pump inlet.
  • Synthesized pistons of super-hard ceramic.
  • Connecting rods of special alloys with a low attrition coefficient, high wear resistance and high anti-seize properties.
  • A hydraulic structure designed to simplify scheduled maintenance procedures (gasket and valve replacement).

During construction the main components manufactured at Interpump's factories are subject to the rigid controls that conform 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 liquids can be pumped?
Interpump pumps have been designed and manufactured to utilize clean, non-salt water at ambient temperatures. However, other types of liquids can be pumped as the experience of 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 us). If the water includes abrasive particles (sand, shavings, etc.) a 20-30 micron grade filter must be installed. The pumps are prepared to pump water up to a temperature of 65°C but for these applications, the pump must be fed a minimum 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 us. Please note that the pumps have not been 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?
Selecting the appropriate pump from our product line normally depends on the flow rate and pressure requirements of the specific application so by using the paired volume/pressure critera it will generally be possible to find a model with the right specifications. If you require any assistance please don't hesitate to contact us. Please note that the pressure level given in the catalogue is the maximum level at which the pump may be used and that there are no restrictions 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 the flow rate is directly proportional to pump speed and can be changed by varyng the r.p.m. The values given in the catalog may be reduced (within a certain limit), but not increased. Also included under the pump specifications is the rating of the motor that will be required as 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 a 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 a flow rate and/or pressure other than those given in the catalogue the motor power can be recalculated using the the following formula:


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?
The pump must be equipped with a safety valve or regulating valve that may 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 be automatic), regulates the pressure by releasing any excess liquid delivered to maintain the 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 the pressure, a gauge with scale adequate to the 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 accessories for high pressure cleaning (lances, guns, fixed and rotating nozzle heads, etc.) as well as accessories (couplings, flanges, pulleys and gear reducers) that have been developed to facilitate the most common types of pump/motor couplings.

7. Pump installation?
For the correct pump installation, follow these instructions:

Hydraulic connections:

- Using the 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 any connections that could create air pockets must be avoided. Avoid installing components that could cause 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, it must have a greater capacity than the flow rate of the pump and it 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, 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 appear, we suggest that the pump be stopped immediately and the water supply connection checked.

Mechanical installation:

- Using the Interpump flanges, couplings and gear reducers that are available for a range of models ensures correct connections due to the accuracy in the machining of the components. 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 a flange is more difficult. In this case, both the pump and motor are attached to the unit base and before connecting the pump to the 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.

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