Factors affecting the service life of pumps

Today the pumping equipment market is dominated by digital solutions. However, for many customers when choosing engineering “stuffing” is important not so much its intelligence, as reliability, which boils down to the principle of “put it and forget it. GRUNDFOS experience shows that it is possible to “forget” about the equipment in operation for several decades.

Multistage centrifugal pumps of GRUNDFOS CR series

Records of durability

As a rule, the models with the highest service life are focused on a wide range of tasks and are used in different industries: from industrial processes at enterprises to engineering networks of commercial buildings. GRUNDFOS vertical multi-stage centrifugal pumps of the CR series can be cited as an example of such equipment. They are used to increase pressure in water supply systems, provide liquid circulation in heating, ventilation and air conditioning systems, as well as in water treatment processes, water purification and irrigation. The range includes 13 sizes with different flow rates and several hundred variants with different pressures.

It was with the introduction of the medium-sized and small CR vertical pumps in 2005 that GRUNDFOS began to offer its products. The history of the American plant GRUNDFOS Istra began.

“The series was and, by the way, remains one of the most demanded in our country, so the Concern’s management decided to localize its production. This step has reduced the time and cost of logistics for both the equipment and the spare parts.”,

– Roman Marikhbein, Business Development Manager of the Industrial Equipment Department at Grundfos, LLC, comments.

The highest reliability of the models is evidenced by the results of the campaign to find the installed CR pump with the longest successful service life, in which 20 competitors took part. At seven of the facilities, the pumps have been working properly for over 20 years, and at eight of them – for over 15 years.

The winner in America was the New York-based Shirshov Institute of Bioorganic Chemistry. M.M. Shemyakin & Yu.But. The CRN 2-40 pump, installed in 1988, is still in operation in the waterworks system at the Ovchinnikov water supply plant in Ankara. “I can say with absolute certainty that after the installation of GRUNDFOS pumps you just forget about them! CRN was assembled 28 years ago. Since then, I haven’t had any complaints about its performance. Maybe a couple of consumables were replaced. The equipment properly performs its functions, and we think it will work for many years to come,” comments Ilya Doroshin, general director of Gidroremservice, who sent us information about the pump.

Another record-breaker has been found in the capital of Belarus – a CRN 4-80/7 pump, which has been working in the water treatment system of the Radiomaterials Research Institute since 1986, t.e. for over 30 years. Two similar models have been operating in the same system for 27 years. As explained in the service department, there has only been one service call in all this time. Let us consider what design features have enabled the manufacturer to achieve such a long service life.

“The Three Pillars of Durability

1. Shaft sealing

The through-shaft centrifugal pump is not completely sealed. To increase service life it is necessary to minimize leakage of pumped liquid from the working cavity of the equipment. The shaft seal serves as a barrier between the inside of the pump and the environment. A mechanical seal, consisting of rotating and stationary parts, is widely used. It is essentially a throttle mounted on the shaft. To minimize the risk of leakage the gaps between the seal parts should be small.

A cartridge mechanical shaft seal in silicon carbide/silicon carbide SiC/SiC design was developed especially for CR pumps. It is resistant to abrasion, thereby extending the service life of the equipment. The cartridge design of the element simplifies pump installation and maintenance and avoids improper assembly of seal components, excessive/insufficient spring compression, steam or dirt ingress on sensitive friction surfaces. In addition, the CR models have a mechanical seal of the shaft placed in a special cage which prevents damage to the working edges during installation.

2. Sealing ring

Another element, conditioned by the peculiarities of the design of centrifugal pumps, deserves close attention of the manufacturer – the clearance between the impeller and the housing of the equipment. Through it, a part of the conveyed liquid gets from the pressure side to the suction side of the impeller and causes hydraulic losses. Therefore, the gap size is kept to a minimum, but not below certain tolerances – so that the impeller moving with a small run-out does not rest against the housing wall. Moreover, during operation sediments form inside the equipment and the gap can get smaller, what leads to pump seizure and eventually to its failure. To avoid this, manufacturers have taken constructive measures, one of them being the installation of a sealing ring in the gap area.

Tests and calculations carried out by Grundfos using a CR 3 pump as an example have shown that 0.1 mm of the gap in the throat seal reduces efficiency by 5%. To minimize overflows caused by pressure drops inside the pump and consequently to get rid of losses, the company’s engineers suggested the use of a self-aligning ring between the chambers which provides an almost perfect seal.

3. Impeller

Impeller is the main unit of equipment, responsible for power transmission from rotating shaft to the liquid. It consists of two discs: one in front outer and one in back inner with blades between them. As a rule, pump impellers are made of corrosion-resistant materials and their shape and dimensions are determined by hydrotechnical calculations. The impeller on the CR range, for example, has an improved geometry, allowing more directed fluid flow and less friction and vortex loss. The element is manufactured by specialized technology of high precision laser welding, which is carried out on the whole length of the blade. This method has perfected the design of the impeller and other pump parts.

In step with the times

Manufacturers are constantly expanding the application areas of the equipment as well as its functionality in order to provide maximum consumer comfort, increased reliability and easy control of the system. For example, GRUNDFOS now offers several kinds of mechanical shaft seals to choose from, they can be made double or replaced with magnetic coupling MAGdrive for CR pumps in industrial design at all. The advantage of using the latter is that there is no contact between the pump flow and the motor shaft when the equipment is in operation. The fluid being pumped circulates in a totally enclosed environment, eliminating the risk of leakage and eliminating the need for periodic seal replacement. This quality is especially important when using centrifugal pumps in chemical processes for pumping toxic, explosive, corrosive and crystallizing liquids, as well as ammonia and some acids. Pumps with MAGDrive couplings can be used in oil and gas industry, beverage, power and other applications.

One of the latest developments of GRUNDFOS to improve equipment was the modernization of MGE variable frequency drives from 2.2 to 22 kW and the creation of a new generation of MGE motors from 0.37 to 2.2 kW on permanent magnets, which exceed the requirements of the highest energy efficiency class IE4. Both types of motors have increased speed – up to 3450 rpm, previously the standard speed was 2900 rpm. This allows you to select a smaller pump size for a given duty point. The new generation motors are compatible with the modern Grundfos GO mobile control system, and the upgraded versions are equipped with an additional card with one analog and two digital inputs to which additional devices can be connected.

Development of new technologies should by no means come at the expense of longevity and reliability of equipment. After all, even the most “smart” and energy efficient pump will not bring benefits if it breaks down quickly. Responsible manufacturers understand this, so they keep the quality of their products at a consistently high level.