There are many different definitions of the word "heavy" in the dictionary, including "having a lot of weight" and "requiring a lot of effort". If we look at this term in the context of pumping equipment, the word "heavy" has two meanings: the characteristic of the product to be pumped and the conditions in which the pump will operate. It is worth noting that these concepts are not mutually exclusive, and quite often PD pumps pump heavy product in difficult conditions.
When selecting a pump for heavy product handling or harsh environments, the following should be considered:
- Why are the conditions or the product to be handled by the pump difficult?
- What problems can a pump have in a heavy-duty application?
- What type of pump is best suited to the product and the conditions in which it will be used?
Let's answer the third question first. For more than 50 years, one of the few pump types that has been able to handle both heavy products and harsh environments is the pneumatic diaphragm pump. The PD pump is a positive displacement pump based on the reciprocating operation of diaphragms. Very few parts of the PD pump come into contact with the product during operation - 2 diaphragms, 2 balls closing the inlet, 2 balls closing the outlet, and the walls of the pump's working chamber - and the pump is pneumatic and does not have a permanently heated shaft. These design features allow the pump to be used for idle operation without significant damage and allows the pump to suck product up to 21 feet (6.4 metres) away from the pump, creating positive self-priming characteristics when required and pumping product with abrasive particles up to 34.9 mm in diameter. When combined, diaphragm pumps outperform many other pump types - including internal and external gear pumps, cam pumps, screw pumps and piston pumps - when it comes to heavy-duty applications.
Let's take a closer look at the indicators to consider when it comes to pumping a heavy product. For example, if you need to pump a toxic biocide, you need to choose a PD pump whose elastomers are compatible with the product.
Pump diaphragms, balls, seats and seals (o-rings) are often the only elastomers in a positive displacement pump. There are 3 types of elastomers in positive displacement pumps - rubber compounds, thermoplastic and polytetrafluoroethylene (PTFE), more commonly known as Teflon®. Rubber compounds are made up of rubber and artificial additives that are designed to increase resistance to a specific set of fluids. Thermoplastic is a completely man-made compound created specifically to increase the physical strength of elastomers while making them sufficiently resistant to most acids and alkalis. Teflon is the most inert man-made element and allows for a significantly increased number of applications for pneumatic diaphragm pumps.
As Teflon is an inelastic material, Teflon diaphragms need to be fitted with additional elastic diaphragms to extend the service life of the pump.
Most positive displacement pumps are designed to be used in almost any application, thanks to the ability to match elastomers to any product. The correct selection of elastomers requires knowledge of the chemical compatibility, temperature, abrasive content of the product, as well as the self-priming requirements and sanitary standards that the pump must meet.
When selecting a positive displacement pump, it is also important to know the solids characteristics of the product. When pumping highly abrasive particles, there is a chance that the pump's working chamber could be damaged, resulting in product leakage. The physical wear resistance of the pump is therefore a very important characteristic in heavy-duty applications.
The type of pump connection is also an important feature. The pump can be bolted or clamped. The clamp connection is more popular nowadays, but in cases where aggressive products are pumped, the bolted connection comes to the fore. It is also necessary to take into account the temperature of the pumped product and know the required pressure characteristics. As a standard, PD pumps operate in a 1:1 ratio, meaning that the diaphragm that feeds the product creates a pressure equal to the vacuum created by the second diaphragm in the second working chamber. However, in some applications, the pressure/discharge ratio can be as high as 3:1 or more.
External factors
The most obvious external factor is temperature. Most PD pumps are used in both the cold conditions of the north and the hot conditions of Africa. PD pumps can be made of either metal or plastic. While plastic pumps are widely used in controlled environments (indoor), metal pumps are used in high or low temperature environments. It is also necessary to take into account the product being pumped, for example, when pumping water in winter, a thermal jacket must be installed on the pump to prevent it from freezing inside the pump. In conditions of high temperatures or sandstorms, special protective structures are installed around the pump to prevent overheating or clogging of the equipment.
In addition to the product being pumped, the ambient temperature also has an impact on the elastomers. For example, Teflon is used at extremely low or high temperatures, EPDM is ideal for low temperatures and Viton is particularly effective at extremely high temperatures. The presence of chemicals in the air should also be taken into account, as certain chemical compounds can adversely affect the pump casing and lead to pump failure.
In addition to the casing and wetted parts, the effect of different conditions on the air distribution system of the pump is also worth considering. The higher the temperature of the air, the more moisture it contains. This means that when warm air enters the air distribution system from the compressor, moisture is carried along with it; when the air reaches the pump from the compressor, it cools down, and in some situations the air temperature can even drop to -22ºC. At this temperature, most liquids crystallise, so it is always necessary to pre-dry the air before it is fed to the pump.
For example, a typical August temperature in Louisiana can reach 38ºC with 90% relative humidity. Under these conditions, along with 1,000 cubic feet of air per minute, the pump will pump 460.8 gallons (1.744 litres) of water through the air distribution system. To prevent water from being pumped through the air distribution system, special dehumidification systems must be installed.
The importance of choosing the right pump
Having listed the main elements of heavy-duty applications, we can now move on to consider the problems that can arise if the pump is not selected correctly. When selecting a pump, you should always choose a pump with a slightly higher flow rate, as this will extend the life of the main components of the pump, while reducing repair costs and air consumption. By underestimating the problem, you automatically reduce the pump's efficiency and performance. Also, the product may be viscous and a small pump will not be able to create enough pressure to transport it when pumping expensive products. This can lead to quite large losses associated with the downtime of the production line.
In addition to the costs associated with pump repairs and line downtime, the wrong elastomer material selection can result in a pump that is under maintenance most of the time, as the wetted parts of the pump are constantly damaged.
In the end, the plant technicians always aim to install the pump and forget about it until the date of the pre-scheduled maintenance. That's why experienced engineers often choose pneumatic diaphragm pumps for heavy-duty applications.
The advantages of PD pumps are:
- Absence of seals.
- Ability to work in idle mode.
- Long uptime between failures.
- Good self-priming.
- Pumping relatively viscous products.
- Pumping abrasive products.
- Relatively cheap.
- Lightweight and portable.
- It can be used in explosive and fire hazardous areas.
- Suitable for relatively gentle pumping.
The combined characteristics of PD pumps make them the ideal solution for heavy duty applications.
