KNOLL Maschinenbau GmbH Schwarzachstraße 20
D-88348 Bad Saulgau

Tel.+49 (0) 7581/2008-0
Fax+49 (0) 7581/2008-90318

Contact form

Further information

Press release

Frequency control for cooling lubricant pumps - is it worth it?

KNOLL E-Pass gives you clarity in an hour


Saving energy is one of the crucial themes in the field of metalworking as a whole. However, changes are only made when they bring economic benefit. KNOLL Maschinenbau in Bad Saulgau has developed the E-Pass, a way to test cooling lubricant systems at machines during operation. An hour later, the customer knows whether it makes economical sense to upgrade to a high-pressure pump with frequency control.


KNOLL Maschinenbau, a specialist for conveyors, filters and pumps cooling lubricants and chips, pays particular attention to low power consumption in its cooling lubricant systems. In-house examinations and research have revealed significant potential for power savings in the overall cooling lubricant system, and these can be achieved with precision engineering and through the implementation of tailored components. In some cases, the amortisation times are as low as one year.

Significant energy-saving potential is to be found in the pumps used to supply cooling lubricants under high pressure to the machine tools. KNOLL KTS screw spindle pump is such a self-priming positive-displacement pump. It is characterized by low pulsation, high efficiency and a long life. It requires least energy when equipped with a frequency-control system - called PQ-Tronic at KNOLL (see box) - that varies the pressure (P) and flow (Q) for an optimized speed setting. Compared to a pump with a fixed pressure limiting valve, the user can in this way save up to 70 % on energy consumption.

Electronic control saves energy and is easier on the pump

The frequency-controlled drive for the pump also reduces thermal transfer to the cooling lubricant and into the surrounding air. Moreover, optimized operation is easier on the pump, thereby increasing its service life.

Users can now obtain the benefits of an electronic control for pressure and volumetric flow not only on new systems. Existing cooling lubricant systems can also be retrofitted with frequency converters. The only question is: Does it make economic sense? Savings namely depend on a variety of factors: for example, the machine and the pump running times, the type of machining and types of tools used, the electricity price, and so on. Heiko Stern, product manager for screw spindle pumps at KNOLL knows the problem well: "Production processes are usually complex and require a customized solution for each company. Up to now it was difficult to evaluate the particular process accurately and produce a concrete amortization analysis."

Up to now - because that is what KNOLL is there for: to solve problems. In this case, Heiko Stern's service colleague Jochen Blersch took on the task. He developed the KNOLL E-Pass, as it is termed, a method that can be used to determine the important data at the cooling lubricant system within the shortest period of time, and largely during operation. A software program then calculates how long it would take for a retrofit frequency control to pay for itself.

Questionnaire as a preliminary test

Jochen Blersch points out a preliminary stage of the E-Pass: "Based on our experience, we have developed a simple five-point questionnaire to establish whether or not the E-Pass is worthwhile. All the questions can be answered with "Yes" or "No". Three or more "Yes" answers mean that the test is worthwhile; with five times "Yes", you can be sure that retrofitting makes economical sense, even without testing."

Good examples for frequency control are often found in the cutting of parts made of die-cast aluminium. Heiko Stern explains: "Numerous tools that require high-pressure interior cooling are in use here. The pressure needed changes depending on the tool as machining progresses. Also, there are may companies who machine the same workpieces or workpiece families the whole year round."

The operating time of a high-pressure pump is actually an important factor when it comes to achieving an amortization time of approx. 12 to 24 months, as is the target in most cases. Ideally, the machine should be running in three shifts, i.e. between 6000 and 8000 operating hours a year. The pump design is always based on the tool that needs the highest pressure and greatest volumetric flow. Smaller tools, for example drills, can cope with much less pump performance for the cooling lubricant, which means that they can receive an optimal supply at lower speeds. With a frequency-controlled pump, this saves energy, since the rule of thumb is: half the speed cuts kW consumption by half. When the pressure limitation valve is set to a fixed value, this energy is lost in the form of heat.

E-Pass uses real-world values

If the results of the questionnaire recommend the KNOLL E-Pass, a pump specialist visits the user on site, and takes a look at a machine that is used to produce a typical workpiece. This machine must be shut down for approx. 15 minutes to install a measuring turbine. In addition, the data required (such as operating hours, electricity and investment costs for upgrading) are entered into the computer. The turbine then measures the actual cooling lubricant throughput to the machine and the corresponding pressure during a complete machining cycle.

On completion of the measurement, the difference between the rated speed and the fixed speed is calculated to produce the biggest portion of the energy saving. If a cooling system is connected to the machine, or the hall is air-conditioned, the program also considers the potential saving that frequency control would achieve for cooling.

Little effort - clear results

Just a few minutes after completion of the measurement, a printout is produced showing concrete figures on potential savings and amortization periods. Jochen Blersch points out a further benefit of the measuring procedure: "The data acquired permit an evaluation of the condition of the high-pressure pump, which can also be replaced if necessary when retrofitting the frequency controller."

The costs of retrofitting a frequency controller are reasonable. If the cabinet still has enough space, it is installed there. Otherwise, there is always room somewhere at the machine to attach a suitable support.


PQ-Tronic speed control

KNOLL PQ-Tronic permits the specification of any pressure level in the range from 0 to 150 bar. This system automatically controls the pump performance. Frequency control for the drive motor changes the speed, and consequently the performance, of the pump unit (up to 4500 rpm). A pressure sensor combined with an electronic PID control guarantees the stipulated pressure (setpoint) independently of the consumption. This brings numerous benefits:

  • Energy savings between 50% and 70%
  • Pressure pre-election via M function
  • Low-pulsation supply
  • Soft starts and stops
  • No start-up current peaks
  • Speed adaptation to minimize noise
  • Minimal wear
  • Reduced thermal transfer to the medium




It pays off to examine the cooling lubricant management system for energy saving options. 

Life cycle costs of pumps

The KTS screw pump from KNOLL, for example, is a self-priming positive displacement pump,characterised by low pulsation, high efficiency and a long service life.

The machining of such a gearbox housing is a good example for frequency control for cooling lubricant pumps. Photograph: GROB-WERKE GmbH & Co. KG, Mindelheim, Germany

Even when cutting such a cylinder crank case, it makes sense to use a frequency-controlled cooling lubricant pump. Photograph: MAG IAS GmbH, Eislingen/Fils, Germany