How to choose a pressure switch and which one is better?

Today there are many devices on the market that allow you to automatically control the operation of various equipment, whether it is a pump, compressor, or refrigerator, etc. In the common people, these devices are called a pressure switch or a circuit breaker, more scientifically they are manostats or pressure switches.

The content of the article:

  • Relay types
  • Condor - the inventor of the relay
  • What to look for when choosing
  • The principle of operation on the example of the Condor relay
  • Reviews of well-known relays on the market (Grunfoss, Danfoss, Italtecnica, Unipump, etc.)
    • Advantages and disadvantages of relays of different brands
  • TOP relay for water (application depending on equipment and tasks)
    • CONDOR MDR 5/5
    • CONDOR MDR 5/8
    • CONDOR MDR F4 (FF 4 4)
    • CONDOR MDR F8 (FF 4 8)
    • CONDOR MDR 21/6
    • CONDOR MDR 1/6
  • Conclusion - savings should be reasonable

Relay types

Basically, pressure switches are divided by type:

  • mechanical relays;
  • electronic relays.

Each type of relay has its purpose, and each has its pros and cons. There are many discussions on the Internet regarding their comparison with a detailed description of the principles of operation.

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As for the relay for water, most experts still tend to install mechanical relays, because they are more reliable, simpler and, of course, cheaper than their electronic counterparts, which are quieter and aesthetic. And in the example with compressors, relays are installed only on piston models (up to 15kW). More complex and industrial models are equipped with controllers (electronic compressor control system).

In this article, we will consider what a mechanical relay is and answer questions related to the selection, configuration and further maintenance of this device.

Condor - the inventor of the relay

The design of all relays is approximately the same. To understand the principle of operation and all the nuances of mechanical type adjustment, let's take, for example, a pressure switch from the company CONDOR (Germany)which help to automate water supply.

Why CONDOR? Yes, everything is simple. Because it was this German company that in 1935 received the world's first patent for a membrane pressure regulator for automatic control of pumps. In other words, CONDOR is the first inventor of the pressure switch, and to this day it is the market leader in the development and production in the field of pressure switches, as well as control and management systems for electronic devices and devices.

The Condor company was founded in 1893 as an engineering factory. Now it has the widest range of pressure switch options for working with air, water and other chemical compounds. There are models with working pressure from 0.5 bar to 250 and with temperatures up to 200 °C.

There are many types of relays, such as power relays (directly open or close the motor power circuit in depending on the pressure in the system), and control (when closing or opening the circuit they force the devices to work launch).

CONDOR production is certified according to DIN ISO 9003 in 1993 and according to DIN ISO 9001 in 1995. This company is one of the few whose products are certified for electrical safety and explosion safety, as well as for fire safety.

Has certificates:

  • KEMA;
  • VDS;
  • ATEX (EX).

Condor manufactures relays for many famous pump factories and brands (such as Grundfos, WaterSpray, etc.) as well as the most famous compressor brands (Atlas Copco, Kaiser, Fini, etc.).

What to look for when choosing

To make the best choice, you can contact the specialists of the company Rutector. They have been representing the interests of Condor in Russia for more than 20 years, and they will help with a competent selection.

When choosing independently, we recommend paying attention to the minimum and maximum pressure thresholds, as well as the adjustment range (on / off delta). And, of course, the switching load (voltage, number of phases and current strength) will be an important aspect.

Be sure to consider the installation location and, accordingly, the level of moisture protection of the relay, the connecting dimensions. There is a useful video on how to choose the right relay, everything is disassembled “by syllables” in great detail and in simple words.

The principle of operation on the example of the Condor relay

The principle of operation of a mechanical relay is simple and practically the same for all manufacturers. There is a myth that German CONDOR relays are difficult to set up. Not at all. The setting is similar to a cheap Chinese relay, of which there are a lot on the market under different brands.

The difference is in the quality of the silver-plated contacts (which will not stick), high-strength membrane (made of Hytrel® nitrile rubber from DuPont®), and fine tuning (for example, the MDR F relay, where the lower threshold is only 0.3 bar and the ability to adjust the delta is less than 0.2 bar).

The main working element of the relay after the contacts is a membrane that interacts with the medium (in the case of controlling the operation of the pump, with water). The membrane transmits force to a metal plate resting against the springs. Through compression, a large spring is responsible for the pressure thresholds - turning on and off, and a small one is responsible for adjusting the delta of turning the pump on and off.

Reviews of well-known relays on the market (Grunfoss, Danfoss, Italtecnica, Unipump, etc.)

There are many brands on the market now, both well-known and premium, such as Grundfos, Condor, Danfoss, and other Italtecniсa, Unipump, Aquario, Whirlwind and other variations and analogues of the RD5 type (RDM5).

Advantages and disadvantages of relays of different brands

Let's briefly consider the pros and cons of the most popular:

  1. Grundfos is the world's largest pump manufacturer. Several models of pressure switches are sold under the Grundfos brand in Russia. The most popular are FF4-4 and FF4-8. Also in the lineup there are models MDR5 / 5, MDR5 / 8 and MDR21 / 6. Unfortunately, the range is limited, and if you need to select a relay for a higher pressure or choose a model with a different version, you will have to look for such a relay from other manufacturers.
  2. CONDOR (Germany) is the world's leading developer and manufacturer of pressure switches, which are the main product of the company. Full production cycle in Europe. The widest model range, including more than 1000 versions for almost any task and operating conditions in domestic and industrial applications. Due to the wide variety of nomenclature, it may be difficult to independently determine the optimal model, in which case it is recommended to contact a product specialist.
  3. Danfoss (Denmark) is a well-known European manufacturer of high-quality automation equipment, incl. pressure switch. The company is focused on the industrial segment, for this reason the line of pressure switches for domestic use is limited to a few models.
  4. Italtecnika - manufactures pressure switches for single-phase and three-phase pumps.

TOP relay for water (application depending on equipment and tasks)

In order to make it easier to figure out which and when relays are better to use, let's analyze a few live examples of choosing the “right” relays using the popular CONDOR models as an example.


CONDOR MDR 5/5 - operating pressure 1.5 to 5 bar, pressure switch with increased switching capacity for direct connection to the network of three-phase and single-phase pumps. Model for the lazy: set, adjust and forget.

Silver-plated, enlarged and more reliable than other models, contacts are rated for current up to 25A!, which gives a significant margin of switching power and guarantees the absence of sticking even when operating at extreme loads.

The relay is three-pole - this means that three contacts (phases) open at once. This design of the node ensures the safety of the device and increases the resource. Robust sealed housing with a high degree of protection IP 54 allows you to use the pressure switch in almost any environment, including. in rooms with high humidity. The durable flange is made of die-cast aluminum and has a hole for attaching a pressure gauge. For direct connection of three-phase pumps, this model is currently exclusive and the best offer on the market.

Characteristics of CONDOR MDR 5/5:

  • working pressure range: from 1.5 to 5 bar;
  • type: three-pole, normally closed;
  • connection schemes: one and three phases;
  • rated operating current 1’ 240V: 25A;
  • maximum pump motor power: 1’ 240V -2.5kW, 3’ 380V -5.5kW;
  • protection class - IP54;
  • dimensions: 110 X 80 X 177 mm.


CONDOR MDR 5/8 - operating pressure from 2 to 8 bar. Otherwise, this model is similar in design and other characteristics to the MDR 5/5 model.


CONDOR MDR F4 (FF 4 4) - working pressure 0.22-4 bar. The control pressure switch is designed to connect any pump to a control cabinet or starter. It is also possible to use small pumps up to 0.55 kW for direct connection to the network.

The relay is made in a transparent case, equipped with a convenient setting scale, according to which any user without training and a pressure gauge can set the required pressure. It has a high degree of protection against dust and moisture - IP54. Equipped with SPDT contacts that allow the pump to be connected to the control cabinet in a conventional, normally closed circuit (automatic shutdown when the maximum pressure is reached) or normally open circuit (shutdown when the pressure drops, e.g. for protection against dry run).

In switching, this model is almost silent and much quieter than any analogues, it has the finest tuning and the minimum size of the adjustable delta up to 0.15 bar

Characteristics of CONDOR MDR F4 (FF 4 4):

  • working pressure range: from 0.22 to 4 bar;
  • type: control, single-pole 1 SPDT;
  • maximum switching power: 0.55kW;
  • protection class: IP54;
  • dimensions: 104 x 76 x 107 mm.


CONDOR MDR F8 (FF 4 8) - working pressure from 0.5 to 8 bar. Similar in design and other characteristics of the MDR F4 (FF 4 4) model.


CONDOR MDR 21/6 - operating pressure from 1.5 to 6 bar. Simple and reliable pressure switch for direct connection to the network of single-phase pumps up to 2.2 kW. The two-pole contact block simultaneously opens both circuits (phase and zero), which makes the operation of the system safer. The pressure switch has a convenient “on / off” handle for the possibility of manually starting the pump. The scope of supply includes cable glands.

Characteristics of CONDOR MDR 21/6:

  • working pressure range: from 1.5 to 6 bar;
  • type: two-pole, normally closed;
  • wiring diagrams: single phase;
  • rated operating current 1’ 240V: 17A;
  • maximum pump motor power: 2.2kW;
  • protection class - IP44;
  • dimensions: 67 x 96 x 101mm.


CONDOR MDR 1/6 - working pressure up to 6 bar. The most compact and cost-effective relay in the CONDOR range for direct connection to the network of single-phase pumps up to 4 kW. A quality alternative to Chinese relays from the world's leading manufacturer, has a large stock of switching power, manufactured in accordance with European standards for fire and electrical safety. The Hytrel® relay diaphragm is approved by the German regulator for safe use with potable water.

Characteristics of CONDOR MDR 1/6:

  • working pressure range: from 2.5 to 6 bar;
  • type: two-pole, normally closed;
  • wiring diagrams: single phase;
  • maximum pump motor power: 4 kW;
  • rated operating current 1’ 240V: 20A;
  • protection class - IP44;
  • dimensions: 85 x 55 x 65 mm.

Conclusion - savings should be reasonable

All CONDOR devices are tested in a test laboratory for switching accuracy and compliance with electrical safety regulations. The confirmed resource is not less than 500,000 switchings. Even if the pressure switch switches 5 times every hour, this is more than 10 years of operation.

Relays are safe in operation, have 100% protection against short circuit. Permissible operating and medium temperatures from - 5... + 80 ° C. Any user will understand the setting, each relay has an individual instruction with detailed a description of the installation and adjustment in Russian, as well as a QR code on the video on the adjustment of this particular models.

The pressure switch is a small unit on the operation of which the reliability of the entire water supply system depends. When installing an expensive and high-quality pump, keep in mind that insignificant savings in buying a relay pressure from unverified manufacturers can lead to a shutdown of water supply to the house at the most inopportune moment.

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