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, be it a pump, compressor, or refrigerator, etc.In common parlance, these devices are called pressure switches or circuit breakers; more scientifically, they are manostats or pressure switches.

Types of relays

Basically, pressure switches are divided by type:

• mechanical relays;
• electronic relays.

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

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

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

Condor - 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 as an example pressure switches from CONDOR (Germany), which help automate the water supply.

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

Condor was founded in 1893 as an engineering plant. Now its product range includes the widest range of pressure switch options for working with air, water and other chemical compounds. There are models with operating pressures from 0.5 bar to 250 and with temperatures up to 200 °C.

There are many types of relays, both power (they directly open or close the power supply circuit of the electric motor depending on the pressure in the system) and control (when by closing or opening the circuit they force the starting devices to operate).

CONDOR production was 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 and explosion safety, as well as fire safety.

Has certificates:

• KEMA;
• VDS;
• ATEX (EX).

Condor produces relays for many well-known pumping factories and brands (such as Grundfos, WaterSpray, etc.), as well as well-known 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 Rutector company. They have been representing the interests of Condor in Russia for more than 20 years, and will help with competent selection.

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

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

Operating principle using the example of a Condor relay

The operating principle of a mechanical relay is simple and is the same for almost all manufacturers. There is a myth that German CONDOR relays are difficult to configure. Not at all. The setup is similar to a cheap Chinese relay, of which there are many on the market under different brands.

The difference is the quality of the silver-plated contacts (which will not stick), the high-strength membrane (from Du Pont® Hytrel® butadiene-nitrile rubber), and the precise adjustment (for example, the MDR F relay, where the lower threshold is only 0.3 bar and the ability to adjust the delta is less 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 a pump - water). The membrane transmits force to a metal plate that rests on the springs. Through compression, the large spring is responsible for the pressure thresholds - turning on and off, and the small one is responsible for adjusting the delta of turning the pump on and off.

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

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

Advantages and disadvantages of relays of different brands

Let's briefly look at the pros and cons of the most popular ones:

1. Grundfos is the largest pump manufacturer. Several models of pressure switches are sold in Russia under the Grundfos brand. The most popular are FF4-4 and FF4-8. The line also includes 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 design option, 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 company's main product. Full production cycle in Europe. The widest model range, including more than 1000 design options for almost any task and operating conditions in domestic and industrial applications. Due to the wide variety of products, it may be difficult to independently determine the optimal model; in this case, it is recommended to contact a product specialist.
3. Danfoss (Denmark) is a well-known European manufacturer of high-quality automation equipment, including pressure switches. 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 - produces 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 understand which and when relays are best used, we will look at several live examples of selecting the “right” relays using the example of popular CONDOR models.

CONDOR MDR 5/5

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. A model for the lazy: install, adjust and forget.

Silver-plated, enlarged and more reliable compared to other models, the contacts are designed for a current of up to 25A!, which provides a significant reserve of switching power and guarantees no 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 unit ensures the safety of the device and increases the service life. A durable sealed housing with a high degree of protection IP 54 allows the pressure switch to be used in almost any conditions, including in rooms with high humidity. The durable flange is made of cast aluminum and has a hole for attaching a pressure gauge. For direct connection of three-phase pumps, this model is today the exclusive and best offer on the market.

Characteristics of CONDOR MDR 5/5:

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

CONDOR MDR 5/8

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)

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

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

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

Characteristics of CONDOR MDR F4 (FF 4 4):

• operating 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)

CONDOR MDR F8 (FF 4 8) – operating pressure from 0.5 to 8 bar. The design and other characteristics of the MDR F4 (FF 4 4) model are similar.

CONDOR MDR 21/6

CONDOR MDR 21/6 – operating pressure from 1.5 to 6 bar. A simple and reliable pressure switch for direct connection to the network of single-phase pumps with a power of up to 2.2 kW. The two-pole contact block simultaneously opens both circuits (phase and zero), which makes operation of the system safer. The pressure switch has a convenient “on/off” handle for manual start of the pump.Cable glands are included in the delivery.

Characteristics of CONDOR MDR 21/6:

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

CONDOR MDR 1/6

CONDOR MDR 1/6 – operating pressure up to 6 bar. The most compact and cost-effective relay in the CONDOR line for direct connection to the network of single-phase pumps with a power of up to 4 kW. A high-quality alternative to Chinese relays from a leading global manufacturer, it has a large supply of switching power, and is manufactured in accordance with European fire and electrical safety standards. The Hytrel® relay membrane is approved by the German regulator for safe use with drinking water.

Characteristics of CONDOR MDR 1/6:

• operating pressure range: from 2.5 to 6 bar;
• type: two-pole, normally closed;
• connection 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. Confirmed resource of at least 500,000 switchings. Even if the pressure switch switches 5 times every hour, this is more than 10 years of operation.

The relays are safe to operate and have 100% short circuit protection. Permissible operating and ambient temperatures from - 5...+ 80 °C.Any user can understand the setup; each relay has individual instructions with a detailed description of installation and adjustment in Russian, as well as a QR code on the video for adjusting this particular model.

A 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 purchasing a pressure switch from unverified manufacturers can lead to stopping the water supply to the house at the most inopportune moment.