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

Understanding the Causes of Pump Shaft Breakage

By NTS. Pump shafts are essential in many industrial and commercial applications, providing the necessary mechanical force to move fluids through pipelines and process systems. However, when a pump shaft breaks, it can cause significant downtime, production losses, and safety risks. In this article, we will explore the common causes of pump shaft breakage and how to prevent it from occurring. 1. Excessive Load  The most common cause of pump shaft breakage is excessive load. When a pump is overloaded, it places a significant amount of stress on the shaft, causing it to bend, warp, or break. Overloading can be caused by a variety of factors such as a clogged discharge line, worn impeller, or damaged bearings. Proper maintenance, regular inspections, and monitoring of the pump's performance can help prevent overloading. 2. Misalignment  If the pump and motor are not properly aligned, it can cause stress on the pump shaft and lead to breakage. Misalignment can occur due ...
Post a Comment
[Read more...]

Why Pump Shafts Often Break at the Keyway Area

By NTS Pump shaft failure can lead to significant downtime and repair costs in industrial plants. One of the most common locations for pump shaft failure is at the keyway area. In this article, we will explore the reasons why pump shafts often break at the keyway and what can be done to prevent such failures. The keyway is a high-stress point (weakest point)  on the shaft, where a key is inserted to transmit torque between the shaft and the pump impeller or coupling. During operation, the keyway experiences cyclic loading that creates a bending moment in the shaft, which is concentrated in the keyway area. Over time, this cyclic loading can cause fatigue failure in the shaft material, leading to a fracture at the keyway. In addition to cyclic loading, other factors can contribute to shaft failure at the keyway. Improper keyway design or installation can lead to stress concentrations or inadequate clearance between the key and keyway . Misalignment or overloading can also cause ex...
Post a Comment
[Read more...]

John Crane's Type 28 Dry Gas Seals: How Does It Work?

How Does It Work? Highest Pressure Non-Contacting, Dry-Running Gas Seal Type 28 compressor dry-running gas seals have been the industry standard since the early 1980s for gas-handling turbomachinery. Supported by John Crane's patented design features, these seals are non-contacting in operation. During dynamic operation, the mating ring/seat and primary ring/face maintain a sealing gap of approximately 0.0002 in./5 microns, thereby eliminating wear. These seals eliminate seal oil contamination and reduce maintenance costs and downtime. John Crane's highly engineered Type 28 series gas seals incorporate patented spiral-groove technology, which provides the most efficient method for lifting and maintaining separation of seal faces during dynamic operation. Grooves on one side of the seal face direct gas inward toward a non-grooved portion of the face. The gas flowing across the face generates a pressure that maintains a minute gap between the faces, optimizing flui...
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...]

The 7 guiding principles of a Maintenance 4.0 strategy

Formulating a digital strategy is not easy, but these guidelines can help you get off the sidelines and into the game. By Eitan Vesely and Deddy Lavid (Ben lulu), Presenso It is not uncommon for organizations to struggle with many issues related to digitalization. With the hype around digitalization at fever pitch, it is easy to become overwhelmed by the multitude of options available in the marketplace. But the strongest contributing factor to implementation challenges is a failure to devise a strategy for an extensive period of uncertainty. Formulating a Maintenance 4.0 strategy is not easy. An aggressive strategy based on overinvesting in unproven technologies or a conservative strategy of merely waiting on the sidelines are unrealistic options. Guiding principles The seven guiding principles for a Maintenance 4.0 strategic plan are: 1. Invest based on the business case The primary obligation to shareholders does not change just because of the changes occurring within t...
Post a Comment
[Read more...]