Skip to main content

Dry-Running Sealing Technology: Pump Applications (P2)

Solutions to Common Problems

The operation of a single contacting seal would be difficult with any of the identified problems. A single contacting seal relies on cooling and lubrication from the process liquid being sealed. Any interruption in the cooling and lubrication processes will result in damage to the seal and leakage to the environment.

The non-contacting, dry-running seal is a solution to many of the problems identified by users. An installation to a pump is illustrated in Figure 2. This type of pump seal technology does not require the circulation of liquid for cooling. Instead, a static heat of an inert gas is used to pressurize the space between the seals. Nitrogen gas in normally used to create the barrier between the process liquid and the environment. The gas barrier pressure is normally 20 to 30 psi/1.4 to 2 bar above the seal chamber pressure. 
The spiral groove geometry of the seal face is responsible for lift-off and separation of the seal faces during operation. Since the seal faces are not in contact when the shaft is rotating, the only heat that is generated is that of the shearing gas. For normal pump speeds, a temperature rise at the seal face would be 2ºF to 4ºF/-17ºC, compared with several hundred degrees for a contacting seal. This results in a very attractive sealing technology for heat sensitive liquids and those liquids being pumped near their vapor pressure.
This technology represents a solution for those problems that effect cooling and lubrication at the seal faces. These have been identified as loss of seal flush, dry run, start-up without venting, low NPSH and cavitation. Cavitation will also result in the vibration of equipment. The vibration limit for this sealing concept is 0.4 in./s (10 mm/s).

Non-contacting, gas lubricated seals can be used on a wide range of process liquids. If the process fluid contains more than 6% solids by volume, consult John Crane Engineering with specific details about the liquid being sealed. Designs are available for liquids with a concentration of solids to 20% by volume.

With a non-contacting, gas-lubricated seal, rubbing contact at the seal face has been eliminated, so the seal can be operated at the vapor pressure of the liquid being sealed. In addition, there is no limiting factor due to the pressure-velocity relationship and wear at the seal faces. The limiting factor in the application of the seal is pressure that has an effect on seal face deflection.

Dual pressurized, non-contacting, gas lubricated seals have been designed to fit oversized and small bore seal chambers. Oversized bore seal chambers allow for a larger cross section seal, which can handle greater pressures. This original gas seal for pumps, introduced over five years ago, is shown in Figure 2. Many existing pumps in the field have small bore seal chambers and do not require the same pressure capability as the Type 2800 seal. To meet this requirement, the Type 2800E shown in Figure 4 was designed. To meet the need for still higher pressures on pumping applications, with the ability to run dry, the Type 2800HP was designed. This seal fits the same space envelope as the Type 2800 seal and is being used in Petroleum Refining and other industries.
oversized
Benefits

Many users are still struggling to increase MTBPM. Plants that were constructed 20 to 30 years ago were not constructed to today’s more stringent specifications. Deficiencies exist in piping, foundation stiffness, proper NPSH, operations and installation. The competitive edge is being lost at older plants, due to higher costs of equipment ownership and lost production due to equipment down-time.

Non-contacting, gas-lubricated seals are a solution to improving the reliability and efficiency of rotating equipment. They have eliminated seal face wear, heat developed at the seal faces, and are designed to run dry. While trying to solve an emissions problem, this technology has revolutionized pumping systems.

The use of this technology and the absence of a liquid seal support system help to maintain a high degree of product quality, which is necessary in the pharmaceutical and biotech industries. The non-contacting, gas-lubricated seal technology is more forgiving of most operating problems than other seal technologies. The capability of this technology is substantially reducing the cost of ownership of equipment and reducing equipment down-time.

Seal designs shown are patent-protected.
Labels:

Comments

Post a Comment

Popular posts from this blog

Introduction To World of Maintenance

Maintenance has changed Over the last twenty years, maintenance has changed, perhaps more so than any other management discipline. The changes are due to a huge increase in the number and variety of physical assets (plant, equipment and buildings) that must be maintained throughout the world, more complex designs, new maintenance techniques and changing views on maintenance organization and responsibilities.
Post a Comment
[Read more...]

Mastering the Monitoring of Low-Speed Bearings

Machinery that operates at speeds below 600 rpm falls under the category of low-speed machines. These machines are typically large and possess high rotating inertias, making them crucial components of the production line. Although these machines are less prone to breakdowns, they are considered critical, and their failure can result in enormous production losses, significant downtime, and substantial replacement costs. Historically, there has been limited interest in the condition monitoring of these machines due to their infrequent failures. The parts of these machines that necessitate condition monitoring are primarily the bearings and gears in motion. This article will cover modern and innovative techniques for monitoring the condition of low-speed machinery, with a particular emphasis on monitoring the condition of rolling element bearings. Monitoring low-speed bearings present unique challenges. In the case of high-speed bearings, vibration analysis, thermography, and wear deb...
Post a Comment
[Read more...]

Pump Shaft Breakage: Case Studies and Solutions

By NTS Pump shaft breakage is a common issue that can cause costly downtime and repairs in various industries. In this article, we will explore several case studies of pump shaft breakage and the solutions implemented to prevent future failures. Case Study 1: Chemical Processing Plant A chemical processing plant experienced repeated pump shaft breakages in their cooling water pumps. Investigation revealed that the pumps were not properly aligned with the motor and had excessive vibration due to the misalignment. This caused the pump shaft to fatigue and break over time. The problem was resolved by realigning the pumps and installing vibration monitoring equipment to detect any future misalignment or excessive vibration. Case Study 2: Wastewater Treatment Plant A wastewater treatment plant had issues with pump shaft breakage in their sludge pumps. The pumps were designed with a straight shaft and lacked a flexible coupling, causing excessive stress and vibration on the pump sha...
Post a Comment
[Read more...]

Benefits of Remanufacturing bearings

Replacing bearings can prove to be expensive, both in new bearing cost and lost productivity. Some manufacturer takes bearings and expertly remanufactures them to like-new condition for extended service.
Post a Comment
[Read more...]

How To Troubleshoot the Effective Maintenance

Knowledge of effective troubleshooting practices can go a long way toward getting equipment back on line quickly. Unfortunately, due to many reasons troubleshooting occupies too much of a technician's time. You might consider these six key elements to improve your troubleshooting skills: Understand the system Understand the problem and history Eliminate the obvious Develop possible causes and theories Eliminate causes, start with what is easy, or likely Validate and document the solution Firstly, if you do not understand the system and how it functions, you will be thrashing around in the dark. I found the best time to understand was while the equipment was running and producing product. Time spent studying the process while the equipment was running paid huge benefits when issues arose. It was always beneficial to listen closely to what the operator saw, heard, noticed, and did, just before the problem occurred. I learned quickly that a good operator was a great asset. ...
Post a Comment
[Read more...]