Monthly Archives: April 2016

The 5 Must-Read Articles About Pump Efficiency

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Ensuring that a centrifugal pump is running as efficiently as possible requires extensive knowledge of what makes an efficient system, and what factors create efficiency. These five articles are essential for any user of centrifugal pumps.

1. What Is Efficiency?

Efficiency in a machines is defined as how well it converts energy from one form to another. For example, if a machine receives one unit of energy and outputs a half-unit of energy, the efficiency of that machine would be 50%. Unfortunately, the English system of measurements makes efficiency calculations more complex than this example. Read more about efficiency and the use of constraints here.

2. Specific Speed

Specific speed is a confusing subject that people easily get hung up on. But by considering specific speed as an index number to predict pump characteristics, it can be somewhat easier to grasp. Read more about specific speed and how it can be used to select the right pump, and even predict premature failure.

3. The Power of Wear Rings Part Two: Efficiency

Metal wear rings can actually produce a substantial decrease in efficiency, even when they are reduced to the minimum clearance. Unfortunately, metal rings cannot experience a clearance reduction below the minimum without the risk of pump seizure. Read more about how metal wear rings limit pump efficiency here.

Pumps: HP, RPM, and Energy Efficiency

Reducing a pump’s operating speed can help extend the life of its motor and bearings. Even the pump seals will have a longer life span, and the damaging effects of abrasives are reduced. Read more about reducing operating speed to save money on maintenance and reduce downtime.

Gain Efficiency With Volute Design

In radial machinery as well as other applications, a volute is meant to transfer flow from an annular cross section to an exit pipe. Or, a volute might be reversed in a turbine; there are many variations on how this part is used. Read more about the many uses of a volute here.

For even more information about pumps and their components, speak to the experts at Real Seal.

How To Extend Mechanical Seal Life

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If you want to drastically improve the efficiency of your pump and reduce maintenance, the first thing to do is change your approach to maintaining your pump. Focus not just on the specialized equipment your plant uses, but on the pipes, valves, and other pieces which are crucial for the plant’s operation.

Did you know that the most common source of wasted energy in pumping systems has to do with seals that weren’t properly sized for their applications? This causes throttling of the pump’s flow, and reduces efficiency. Pumps run in this way also produce higher levels of vibration, which will cause unnecessary damage and reduce the longevity of the seals significantly.

Where does seal failure begin?

While improvements in mechanical seal design have drastically improved their lifespan, using seals outside of their intended environment will cause them to fall short of these estimates. Oftentimes, the problem is that the pump has been used outside of its desired application range. By taking the time to ensure that the entire system is working properly, and fixing problems at their source, you can reach the best efficiency point (BES) and extend the life of your seals.

Root Causes

If a premature mechanical seal failure occurs, there are several common root causes which should be investigated to reach optimal performance for the whole system. In most cases, sealing devices are are being used in an off-design operation. This can cause excess vibrations transmitted throughout the pump, and damages the seals installed in the system.

Avoid these root causes of seal failure

Excessive vibration in the seal chamber cavitation, internal re-circulation, or asymmetrical wear.
Cavitation refers to the vaporization of the fluid and fluid film in the seal chamber.
Temperature increases in the seal chamber under low-flow conditions will cause vaporization of the fluid in the seal chamber.
Insufficient cooling flow from mechanical seal support system.

Critical Seal Components


The mating pair of seal rings is the most sensitive to vibration and insufficient lubrication. Choose these rings carefully based on the conditions of the sealed environment, including the temperature and surface pressures involved. These conditions can change quickly when the seal is exposed to vibration or lacks the sufficient lubrication. Sealing systems try to compensate for changing interface conditions, but off design pump operations may damage the seal if it is forced into a setting it was not intended for. Be wary of more subtle damage which may result from leakage at the seal interface. The cause of this may be unrelated to the material of the seal or its design.

By taking a more involved approach in the subsystems of your pump, you can save money on seal maintenance and improve its overall efficiency. To purchase mechanical seals and other gaskets, visit Real Seal.

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Making Sense of O-Ring Materials

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There’s no denying that choosing an O-Ring is a daunting decision for newcomers. Just take a look at this website designed to simplify the O-Ring selection. While this website does a great job of compiling O-Ring-related information into a single, easily digestible place, there are simply simply a large number of factors that relate to your O-Ring selection. Understanding the benefits of each material Real Seal provides for your application will make your decision much easier. This blog has already covered silicone more in-depth, so please take a look if you can’t find a material that suits your application here.

EPDM

Ethylene propylene diene monomer rubber, or EPDM, is a versatile material used in a wide variety of applications. It provides excellent resistance to a wide variety of application factors, including: steam, water, heat, ozone, sunlight, mild acidics, alkali, and oxygenated solvents.

EPDM may also be cured with sulphur or peroxide if your application requires it. Real Seal focuses on peroxide-cured EPDM, since peroxide provides better chemical and thermal resistance compared with sulphur. Peroxide-cured EPDM resists up to 150 C (300 F), while sulphur can only resist up to 120 C (250 F). For this reason, peroxide is recommended for applications seeing heavy use.

Peroxide-cured EPDM will improve the heat stability, modulus (elastic stiffness), aging, and compression of the O-Ring. It will be resistant to the following common substances:

  • Alcohols
  • Engine coolant
  • Hot water
  • Ketones
  • Organic and inorganic acid

However, it cannot be used with fuels, greases, or mineral oils. If your application involves drinking water, food, or beverages, peroxide-cured EPDM will likely be the best material.

Poyurethane

Polyurethane is a thermoplastic resin which also has elastometric properties. You may recognize polyurethane in various materials around your home. But its unique properties – such as the highest tensile strength and resistance (i.e. to abrasion and tear) of any elastomer – has allowed it to carved out a special niche as an O-Ring or seal as well. Most polyurethanes will work in temperatures ranging from -40 C to 82 C.

Real Seal also offers variant of polyurethane called polyester-polyurethane (AU) and polyether-polyurethane (EU). Within a temperature range of -40 C to 82 C, AU can resist hydrocarbon fuels, oxygen, ozone, and weathering well. AU also features improved abrasion, heat, and oil resistance; however, it deteriorates quickly when exposed to acids, ketones, and chlorinated hydrocarbons.

EU is more resistant to water and humidity than other polyurethanes. Its toughness and abrasion resistance also make it very suitable for hydraulic systems where high pressures, shock loads, wide metal tolerances, and abrasive contamination are involved.

NBR/Nitrile

Acrylonitrile butadiene rubber is also called simply Nitrile or NBR. This elastomer is a great choice for a seal in most hydraulic and pneumatic applications, since it can handle compression set, tear, and abrasion better than most other elastomers. The only downside is that it must be protected from sunlight, though it may resist sunlight better if it is compounded with hydrogenation, carboxylic acid addition, or another substance.
It is used with a wide variety of substances:

  • Fluids
  • Fats
  • Animal and vegetable oils
  • Flame retardant liquids (HFA, HFB, HFC)
  • Grease
  • Water
  • Air

HNBR

Hydrogenated nitrile rubber, or HNBR, is similar to NBR, but with better resistance to oil and chemicals, and temperatures up to 150 C. NBR, by contrast, may be used between -35 C and 120 C. HNBR is typically used in rubber moulded parts, O-rings, and dynamic seals, as well as high-tensile strength and abrasion applications such as:

  • Mud motors
  • Rotary steerable tools
  • Measurement While Drilling (MWD)
  • Logging While Drilling (LWD)

FKM

Fluorocarbon rubber is a rubber compound with high chemical resistance, as well as low compression set at elevated temperatures. Though FKM cannot be used with bases, it is compatible with applications involving:

  • Mineral oils and greases
  • Aliphatic
  • Aromatic and chlorinated hydrocarbons
  • Fuels
  • Oils
  • Silicone oils and greases

FFKM

FFKM is essentially FKM with a fully fluorinated polymer backbone that offers superior thermo-chemical resistance. This allows it to be used in most harsh environments, including hot amines, steam, solvents, and hydrocarbons. The downside is that its resistance to lower temperatures is poor.

Aflas/FEPM

Aflas has a chemical structure with excellent heat resistance, chemical resistance, and electrical resistivity. It can also resist chemicals like acids, alkalis, steam, as well as other strong bases (unlike FKM). It does, however, have a weakness to low temperatures in aromatic oils, and poor resistance to mineral oils. It can be used in temperatures from -5 C to 200 C.

No matter what material you need, Real Seal will have the material perfect for your application. Keep checking back here for more information on O-Rings and seals, or contact Real Seal if you have any particular questions.

Component or Cartridge: How to Choose the Right Seal

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In a centrifugal pump, a component or cartridge seal may be interchanged, depending on the application. By understanding the advantages and disadvantages of each, you can ensure the optimal performance of your pump.

Component Mechanical Seals

Most standard mechanical seals fall under this category. Replacements of these seals typically include seal faces, holding brackets, O-rings, boots, and parts which must be installed by an experienced pump technician. This is important, as the seal housing’s limited access requires a precise and accurate hand. If just one component is installed incorrectly, the risk of seal failure will increase significantly. There are many components of the seal which need to be installed just right, including seal faces which must be properly seated on the shaft or seal housing, and sliding O-rings and elastomers over shaft shoulders, key ways, and other parts. A mistake installing any of these parts can result in misalignment, damage, and incorrect seal tension.

Cartridge Mechanical Seals

While cartridge seals share many components in common with component seals, there are a few essential differences. Some of the parts come preassembled, like the stationary components which come in a housing; and the rotating components, which come on a shaft-mounted sleeve and are sealed with an O-ring or elastomer. Because of this, installation errors are far less likely.

A key part of successful seal installation is setting the spring tension. Component seals are set manually by adjusting the length of the seal’s spring. Cartridge mechanical seals, on the other hand, have preset spring tensions. A retaining device is used during the installation process to hold the rotating and stationary elements in alignment.

Whether you will be able to install a cartridge mechanical seal will depend on many complex factors affecting the pump. One of the main factors is which side the seal installs from. Most cartridge mechanical seals cannot be installed on the wet side of a pump’s seal chamber, behind the impeller. These seals are generally incompatible with submersible pumps for a similar reason.

Comparing the Two

Deciding between the two seals largely depends on the cost and ease of installation. While the presence of a competent pump technicians might make ease of installation seem like a non-issue, being able to replace a seal during an emergency outage should be a concern.

Unfortunately, cartridge seals cost two to three times more than component seals, so most competitive repair bids you will see often refer to component seals. Although they cost more upfront, in the long-term, cartridge seals are more cost-effective. While component seals require in-service replacement, cartridge seals require less labor costs and less production lost from seal replacement. You’ll also save money on potential errors resulting from potential installation errors of component seals.

In short, mechanical seals are the best choice for users who need a long-term, cost-effective solution for pump maintenance, while component seals are best-suited for users who place a higher priority on a lower upfront cost. For more information or seals and other related components, visit Real Seal.