Friday, April 15, 2016

To be continued - A Few Simple Principles Guide You To The Best Seal Flush Plan

--- To be continued

3. External Flush

The external flush method is used when it's desirable to isolate the seal from the pumped fluid. However, if you do not have a suitable flushing liquid available or if diluting the pumped fluid with the flushing liquid is unacceptable, this is not an optimal solution. This method consists of a minimal flow of a clean, relatively cool liquid (usually water) from an external source injected into the seal gland flush connection at a pressure higher than the pump seal chamber pressure. The external flushing liquid flows past the seal and into the pump, mixing with the pumped fluid. Usually a flushing liquid pressure of about 10-15 psi above the pump seal chamber pressure is sufficient.

Flow rates of about 0.25-0.50 gpm are typical, but any positive flow is probably adequate unless there is a need for a specific flow rate to keep the seal temperature at a desired level. A restriction bushing or lip seal can be installed at the seal chamber throat to minimize the flush water flow. A control valve, gauge, and flow meter should be installed in the flushing liquid supply line to provide the control functions necessary to set and monitor the flushing liquid supply, with the flow meter being the most important so that a positive flow of flushing liquid into the pump can be confirmed.

An external flush can perform several functions:
  • Flushes damaging solids away from the seal
  • Isolates the seal from the pumped fluid
  • Cools the seal
  • Carries away seal generated heat
  • But, it also has its disadvantages:
  • Additional costs
  • Potential problems may occur when diluting the pumped fluid
  • Possibility of seal failure when the flushing liquid supply is interrupted by system failure or human error


  • 4. Induced Closed Loop Circulation System

    Not common, but may be recommended when it's necessary to control the temperature at the seal to a level different than the pumped fluid. It can only be used with a seal that has special circulating features. The seal must be equipped with a device that generates some circulation flow (basically a small impeller) and piping in and out of the seal chamber through a heat exchanger. In most cases a bypass flush with a heat exchanger would be the more reliable method to obtain the same results, but an induced closed loop circulation system can be used to reduce the heating/cooling load since only a small amount of liquid contained in the seal chamber is circulating through the heat exchanger.

    If you are considering an induced closed loop circulation system contact your local seal supplier to come up with the best system design.

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  • A Few Simple Principles Guide You To The Best Seal Flush Plan - EastMachinery

    Are you Tired to watching your money spiral down the drain from mechanical seal repair or replacement? A few simple principles can guide you to the best seal flush plan for your installed mechanical seal, allowing the seal to operate in an environment that generates optimal seal life yet minimizes costs from water usage and product dilution. Today, we'll identify 4 flush piping plans for single mechanical seals and how they work. In future articles, we'll dive into double mechanical seals and packing, so stay tuned!

    1. No Flush

    Can only be used if the pumped fluid is clean, does not exceed the temperature limits of the seal, is compatible with the seal components, and is in no danger of vaporizing or solidifying when exposed to the additional friction heat generated by the seal. If this plan is used, a tapered or self-venting seal chamber is highly recommended.

    2. Bypass Flush

    This method is used when the pumped fluid is clean, does not exceed the temperature limits of the seal, and is compatible with the seal components. It's not recommended if the pumped fluid contains solids that could adversely affect the seal or if the temperature of the pumped fluid exceeds the maximum temperature for the seal.

    Normally, this method consists of piping run from the pump discharge to the flush connection on the seal gland, providing flow from the pump, past the seal, and back into the pump through the seal chamber throat. It can also be piped from the flush connection on the seal gland back to the pump suction, which would result in the flow going the opposite direction and can have the added benefit of lowering the operating pressure at the seal. If warranted, accessories such as a heat exchanger or pressure reducing orifice can be installed in the piping.

    A bypass flush provides circulation flow past the seal faces to carry away seal generated heat, so the seal operating temperature will stabilize at the temperature of the pumped fluid. This method is simple, reliable, and inexpensive. It does not result in product dilution and is the preferred seal flush method unless there is a specific reason not to use it.

    --- To be continued

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  • EastMachinery Tell you Why Get Low Flow and Pressure From A High Pressure Pump?

    Every facility manager knows that he or she could be held at least partially responsible for periods of reduced productivity and increased downtime. But what happens when a critical high pressure pump doesn't meet performance expectations? Leveraging the skills and expertise of the Crane Engineering team, one manufacturer solved this problem.

    The Manufacturer's Challenge

    A food manufacturing plant in southern Wisconsin specializing in the production and packaging of carrots, corn, mixed vegetables, peas, potatoes, and stew vegetables installed high pressure pumps to supply water to the plant for clean up after a long day of production. The main purpose of these pumps was to supply enough flow and pressure to hoses placed around the plant for cleaning and pressure washing work areas. After these pumps were installed, they still weren't seeing enough flow and pressure to all of the nozzles and hoses placed throughout the plant. This was a problem that needed to be addressed.

    The company was running three (3) Roto-Jet high pressure pumps in parallel to supply flow and pressure to the plant. Many food manufacturing plants, including this one, use fixed flow orifices on the discharge of the pump to protect it from running off the curve and destroying the pump, which could be detrimental in terms of maintenance costs and unscheduled downtime for the company.

    Why A Fixed Flow Orifice Is Not Appropriate

    Using the fixed flow orifice on the discharge of the pump causes a significant amount of wasted energy and places limitations on the capacity and production of the pump.

    In coordination with the facility's maintenance department, it was decided to provide a long-term, more substantial solution by removing the orifices and sticking with the standard size discharge. The team at Crane Engineering then sized, selected, and installed a pressure regulating valve in the discharge of the pump with a controller to regulate the valve. This allowed for full control of the high pressure pumps, while increasing flow rate and discharge pressure throughout the plant. Problem solved!

    Benefits of the Pressure Regulator and Controller Setup

    Using the pressure regulator and controller setup versus the flow orifice helped to increase productivity, and also ensured consistency across the board for higher flow rates and pressure for which the pump was initially designed.

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  • Wednesday, April 13, 2016

    How A Paper Mill Found the Right Mechanical Seal for A Pulper - EastMachinery

    Is there anything tougher to seal than a bottom entering pulper? Rotors on these machines take a beating from market pulp bales and recycled material, causing large radial shaft deflections. Traditionally, seals have been packed, allowing for leakage, loss of product, wet floors, and thousands of dollars wasted on downtime and gearbox repair.
    The maintenance department at New Page decided they weren't going to take it anymore. The leaking seal on "Slab Broke Pulper" was simply costing them too much. They determined that the seal they needed would have to be fast and easy to install, very low maintenance, and withstand the heavy shock and vibration that occurs during normal operating conditions.
    New Page decided to install a John Crane fully split mechanical seal with compression ring rubber bellows. The rubber bellows would add flexibility and shaft deflection so angular misalignment and run outs were tolerated.
    The mechanical seal they chose accepted:
    • Radial shaft movement of 0.125"
    • Shaft run out up to 0.020"
    • Stuffing box waviness up to 0.030"
    • Axial end play up to 0.060"
    • Out of squareness box face to the shaft of up to 0.100"
    • Temperatures up to 180° F
    • Pressures up to 80 psig
    • Speeds up to 1,800 rpm
    The maintenance team at New Page placed bets on the number of days the mechanical seal would survive, confident the harsh operating conditions would cause it to leak.
    But it never did.
    Fast forward 21 years. The maintenance team is again looking at "Slab Broke Pulper" to investigate an issue concerning pulp break-up. They inspect the unit and find that the same John Crane seal installed in the early 90s remained, and still, no leaks.
    Crane Engineering Account Manager Bob Linder, and Service Technician Dave Holtz, along with two of the mill's maintenance people, rebuilt the seal and promptly put it back into service on "Slab Broke Pulper". Two years later, and despite a bent shaft, the mechanical seal continues to perform against leakage, saving the mill thousands in rebuilt gearboxes and time spent re-packing stuffing boxes.


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  • 5 Things You Must Know for Sizing a Pressure Regulator, Correctly!

    A pressure reducing regulator is commonly used to manually control pressure of a liquid, gas or steam. Choosing the right regulator for your application can be challenging. There are 5 variables required to size any pressure regulator and properly calculate Cv: upstream pressure, downstream pressure, flow range, temperature and fluid type. We define each variable and talk about why it's crucial to sizing a pressure regulator.

    Please note: Cv is a coefficient of flow for valve sizing. It's used to quantify valve flow performance and can vary with both size and style of the valve or regulator. Once you calculate the required Cv range, you'll know the valve or regulator is sized correctly to handle the actual flow.

    1. UPSTREAM PRESSURE

    Supply pressure or Inlet pressure. This is the pressure upstream of the regulator. This pressure could be coming off of a main header at 100 psi. If it is a higher pressure, such as 1,000 psi, and your goal is to regulate a much lower pressure, less than 100 psi, then a second regulator may be required to knock down the pressure in two stages: one high pressure regulator and one low pressure regulator.

    2. DOWNSTREAM PRESSURE

    Outlet or Control Pressure set point or range. This is the pressure downstream of the pressure reducing regulator. The pressure levels are what you are attempting to control. It could be a specific pressure point, like 30 psi, or a range of 5 to 20 psi. The difference between upstream and downstream pressure is called a "pressure drop" or "pressure differential".

    3. FLOW RANGE (minimum, maximum and normal)

    It's a good idea to size the regulator at a minimum of 3 separate points in order to get a range of flow requirement. This gives you a safety factor, so the regulator is not over or under-sized.

    4. TEMPERATURE (minimum and maximum)

    Temperature can affect the required Cv. Note that temperature does not affect Cv nearly as much as pressure and flow.

    5. FLUID TYPE

    Determine what fluid is going through the regulator. Is it liquid, gas or steam? What are its properties? Understand that sizing formulas are different for each type of fluid. For example, the formula for critical pressure drop is different than non-critical pressure drop for gases. For steam, you must know whether it's saturated steam or super heated (higher temperature).



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  • Wednesday, April 6, 2016

    Lubrication, Bearing Design Considerations in Medical Technology



    Lubricant selection may be the specification most overlooked by designers and engineers. Bearing life depends on proper lubrication in terms of both type and amount. In many cases, miniature and smaller instrument bearings are lubricated once for the life time of the device. Thousands of greases and oils are available that are designed to function in a variety of conditions and environments.

    Operating temperature is the primary consideration when selecting a lubricant. Temperature directly impacts the base oil's viscosity, which in turn impacts the ability to support loads. In the world of medical devices, bearing lubricants are subjected to sterilization, temperature extremes, high speed rotation, saline wash down or irrigation, chemicals and reagents, blood, and radiation.

    Lubricant selection not only depends on the operating conditions the bearing will face, but may also be subject to regulatory requirements. Manufacturers of medical devices are often required to use what are known as food-grade lubricants, which are broken into categories based on the likelihood they will contact food.

    H1 lubricants are food-grade lubricants used in food processing environments where there is some possibility of incidental food contact. H2 lubricants are used on equipment and machine parts in locations where there is no possibility that the lubricant or lubricated surface contact food. Finally, H3 lubricants, also known as soluble or edible oil, are used to clean and prevent rust on hooks, trolleys, and similar equipment.

    Due to the wide array of products, price and availability, both a lubrication specialist and the bearing manufacturer should be consulted before making a final lubricant selection.

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    Bearing Design Considerations in Medical Technology as Bearing Materials



    All bearings should be manufactured using rings produced from high purity material. For most medical applications, martensitic stainless steel, similar to AISI 440C, is recommended and often required due to regulatory requirements. This material, which can be specified differently depending on its manufacturer, provides for good corrosion resistance and has fine, evenly dispersed carbides which result in lower noise and vibration levels than 440C. This type of stainless steel is very desirable, particularly in high speed devices.

    Nitrogen enhanced martensitic stainless steel is also available, and while it is more expensive it offers up to 5 times the corrosion resistance when compared to traditional "440C type" materials. Other benefits of this material are very low noise levels, extended fatigue life due to its fine structure that contains smaller chromium nitrides (as opposed to chromium carbides) and a high resistance to corrosion resulting from exposure to blood.

    In some cases, balls produced from ceramic materials, such as silicon nitride, can prove beneficial. Ceramic balls are light weight, highly polished, non-magnetic, exhibit high hardness, and resistant to attack from most liquids and chemicals. Ceramic balls greatly improve the high speed capability of the bearing. Bearings made of steel rings and ceramic balls are commonly called hybrid bearings. While ceramic balls have an impressive list of beneficial characteristics for bearing applications, they are not a "cure all" medicine. Due to the high hardness of the ball, contact stress is increased so fatigue life is compromised. So, when the typical failure mode is characterized by fatigue, it's usually best to stick with steel balls.

    Retainers, or ball separators, are typically produced from a 300 series stainless steel. In high speed applications, it is often necessary to use a plastic or phenolic resin "snap-in," or crown, style retainer. For very high speeds, an angular contact bearing with a full machined retainer is recommended. These types of retainers provide increased stability at higher speeds.

    Phenolic resin cages have a porous structure and can be impregnated with oil for additional lubricity. Some of the plastic materials, such as polyamide-imides, contain additives such as graphite and Teflon for additional lubricity in emergency running conditions. A wide array of lightweight plastic material are available, which, can handle temperatures up to 500F and are autoclavable.

    An autoclave is a device used to sterilize surgical tools, dental drills, or other devices by subjecting them to high pressure saturated steam for around 20-30 minutes depending on the size of the load. This is a common practice that can have a negative impact on the bearing materials and lubrication.

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    Tuesday, April 5, 2016

    Corrosion-Resistant Precision Ball Bearings Eastmachinery




    EASTMACHINERY Bearings LLC now offers a range of solutions allowing precision ball bearings to withstand harsh environments, including exposure to moisture, chemicals, high temperatures and vacuum conditions.

    Among the options available are stainless steel (AISI, 440C, AISI 304, SV30) rings and balls; balls made of silicon nitride or titanium-carbide-coated steel; rings specially coated with thin dense chromium (TDC); and special seals, retainer materials and lubricants.

    Applications for these enhanced bearings include thermal processes, chemical processing, hydraulic pumps, vacuum environments, fuel pumps and pharmaceutical and food processing.

    A standard chrome bearing (left) versus an extreme environment, corrosion-resistant bearing (right) following nitric acid testing. The corrosion-resistant bearing showed no signs of corrosion, which meets the design requirement of 0% corrosion in a nitric acid submersion. Alternatively, the chrome steel bearing was severely corroded, and the ball retainer was deteriorated to the point of non-functionality. If the chrome steel bearing was put in service in such an atmosphere, catastrophic failure would occur in <1min.

    You can rely on AST for our applications expertise and our commitment to provide exceptional service and value.  Call us with your next design… we can help with the solution.

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