the initial symptoms indicates the seal problem

Typically, the first symptom will be some level of leakage. This could range from a small tight spray on the outside of the seal that can be felt on the hand to a full spray out of the back of the seal to a continual drip. Another common symptom is a squealing sound that results when the seal cannot maintain a barrier/buffer fluid. Depending on the type of seal and the American Petroleum Institute (API) piping plan, symptoms could also include leaking of process water into the product or material being pumped. This may dilute the process, or it must be treated further down into the system separate contaminants.

What can cause a mechanical seal to leak or fail?

The loss of the liquid film, or lubricant, between the faces of a mechanical seal is the largest cause of seal failure. This usually results due to a lack of maintenance on the seal’s lubricating parts. Sometimes a seal fails because it wasn’t the right type of mechanical seal for the application. Other causes include improper assembly or installation, cavitation, and improper operation of the pump itself.

What can cause the seal to lose lubrication?

Losing lubrication to the mechanical seal faces can result from a number of factors. Some of these include dry start up, suction loss, plugged flush orifice, increased temperature, the wrong balance, or contamination in the cooler, water jacket, or flush lines.⁴

life cycle cost benefit to mechanical seals over regular packing

Initially, a mechanical seal will cost significantly more than packing. However, when all of the maintenance and operation costs are taken into consideration, mechanical seals are the most cost-effective way to efficiently control and seal fluids in a manufacturing process. With packing, there are costs involved in repacking the pump at least twice a year and downtime for repacking. Because packing wears and cuts into the sleeve of the pump, there are potential costs in replacing any worn sleeves. There are also costs from the loss of product that comes from increased leakage with packing. If the product being pumped is hazardous, it must have piping to run to a drain and be treated. What’s more, because of the higher rate of friction, packing consumes more electricity than mechanical seals. If maintained properly, the life cycle of a mechanical seal can be two to three times that of packing.

Let’s look at the energy savings alone. Presume that 10 percent of a 30 HP motor’s horsepower is used in friction against the packing, and one HP equals one kW of energy. The packing then uses three kW per hour of electricity, and at a rate of 8 cents per kW, times the number of hours in a year (8760), the cost of energy using packing is $2,102.40. A mechanical seal uses only 1/6 of the electricity, which would result in a cost of $350.40. The cost savings in terms of energy alone then is $1,752.00.³

mechanical seals differ from regular packing

Like day and night. Conventional packing requires a lubricant so as not to burn up while the shaft is turning on the equipment. Often the material being pumped serves as the lubricant. However, as a result, packing needs to leak a little to function properly. Mechanical seals, on the other hand, can achieve practically a leak-free environment. With tighter environmental emission regulations placed on manufacturers, this becomes even more important.

Packing requires a higher level of attention and maintenance than mechanical seals. Packing must be adjusted and repacked periodically. What’s more, packing tends to wear on pump parts, cutting the shaft or sleeve. With a static “O”-ring mounted to the shaft, mechanical seals will not damage the shaft or sleeve.

How to determine the right seal for my application?

Here are some questions that will help identify the proper mechanical seal for a given application and process:

• What is the temperature range for the process?
• What is the pressure? Suction? Discharge? Stuffing box?
• Is the product viscous? Does it crystallize, solidify, freeze or build up film?
• the product corrosive?
• kind of pump is used in the process?
• size is the pump? What is the pump’s speed?
• What are the shaft and sleeve sizes?
• the pump cavitate or run dry?
• Which mechanical seals are best for a given application?

The best method of specifying the right mechanical seal is to work in cooperation with a knowledgeable representative from your mechanical seal supplier. Take some of the information you’ve developed from the list above, and work with your sales representative to identify the right product and design features.

Generally speaking, a basic, single-cartridge balanced mechanical seal is adequate for applications where stuffing box pressure is less than 300 pounds per square inch (psi), the temperature is less than 400°F, and the shaft size is from 1 inch to 4 inches. Conditions in excess of these parameters, along with other requirements, might necessitate a special seal design. Double cartridge seals are best in processes where temperature and emission control are critical factors. This is typically the case when working with material that is toxic, radioactive, explosive, or is categorized as a pollutant.²

different types of mechanical seals

There are many options, designs, and materials when it comes to mechanical seals. The configuration and features right for you will depend on your application. Perhaps the simplest, yet most traditional type of mechanical seal is the component seal, which is often mounted on the inside of the pump housing, or stuffing box.

Single cartridge mechanical seals are used in processes using non-hazardous, non-corrosive materials. A single cartridge seal is usually located outside the pump housing, and is not exposed to the material or product being pumped.

Double cartridge mechanical seals are mounted separately on the same shaft, outside of the housing, or stuffing box, and provide maximum sealing for potentially hazardous materials, such as slurries, acids, and volatile organic liquids.

The single and double cartridge seals can be designed with a number of features. They come with either single or multiple springs, or bellows. In addition, both the single and double cartridge seals are available in a split design, where the seal comes in two parts that are assembled to surround the shaft. These are mostly seen on large split case pumps.

What are mechanical seals made of?

What are mechanical seals made of?

The materials used in the design of a mechanical seal are determined by the conditions under which it will be operating. The body of a mechanical seal is typically made from stainless steel. The wearing, or contact face of the seal, can be made from a variety of corrosion-resistant materials, such as carbon, glass-filled Teflon, tungsten carbide, and silicon carbide. The other face, the hard face, can be made from ceramic, niresist, tungsten carbide, or silicon carbide. One face rotates, while the other remains stationary. Typically, the nature of the process, the pressure and velocity of the pump, and the temperature the seal is operating in will determine the seal face material.

There is also usually a shaft or sleeve packing. The material used in this element of the seal could be “O”- rings, Teflon wedges, metal bellows, rubber bellows or elastomers such as Viton‚ EPR, Neoprene, or Grafoil packing.

Vertical Turbine Pumps

Pump Application Data

1. DATUM OR GRADE - The elevation of the surface from which the pump is supported.

2. STATIC LIQUID LEVEL - The vertical distance from grade to the liquid level when no liquid is being drawn from the well or source.

3. DRAWDOWN - The distance between the static liquid level and the liquid level when pumping at required capacity.

4. PUMPING LIQUID LEVEL - The vertical distance from grade to liquid level when pumping at rated cap-acity. Pumping liquid level equals static water level plus drawdown.

5. SETTING - The distance from grade to the top of the pump bowl assembly.

6. TPL (TOTAL PUMP LENGTH) - The distance from grade to lowest point of pump.

7. RATED PUMP HEAD - Lift below discharge plus head above discharge plus friction losses in discharge line. This is the head for which the customer is responsible and does not include any losses within the pump.

8. COLUMN AND DISCHARGE HEAD FRICTION LOSS - Head loss in the pump due to friction in the column assembly and discharge head. Friction loss is measured in feet and is dependent upon column size, shaft size, setting, and discharge head size. Values given in appropriate charts in Data Section.

9. BOWL HEAD - Total head which the pump bowl assembly will deliver at the rated capacity. This is curve performance.

10. BOWL EFFICIENCY- The efficiency of the bowl unit only. This value is read directly from the performance curve.

11. BOWL HORSEPOWER- The horsepower - required by the bowls only to deliver a specified capacity against bowl head.

12. TOTAL PUMP HEAD - Rated pump head plus column and discharge head loss. Note: This is new or final bowl head.

13. SHAFT FRICTION LOSS - The horsepower required to turn the lineshaft in the bearings. These values are given in appropriate table in Data Section.

14. PUMP BRAKE HORSEPOWER - Sum of 'bowl horsepower plus shaft loss (and the driver thrust bearing loss under certain conditions).

15. TOTAL PUMP EFFICIENCY (WATER TO WATER) -The efficiency of the complete pump less.the driver, with all pump losses taken into account.

16. OVERALL EFFICIENCY (WIRE TO WATER)-The efficiency of the pump and motor complete. Overall efficiency = total pump efficiency X motor efficiency.

17. SUBMERGENCE-Distance from liquid level to suction bell.