There are a few basic steps no matter the pump type or application that I will cover, and then I will also address the often overlooked details common mistakes that can deliver both people and equipment into pump purgatory. For the purposes of this column, I am speaking only for centrifugal pumps and, unless otherwise noted, the pumps are not self-priming.
Many of these tips and comments are for initial startups commissioning evolutions , but will also deftly apply to the pump you start up every Monday morning. When I am scheduled to supervise a pump startup, I immediately remind myself of one of my old and trusty mnemonic devices.
Over my career, I have often been summoned to the crime scene as the post-disaster forensic pump pathologist. I have witnessed some expensive startup mistakes that could have easily been avoided if only the operator had simply read and observed a few key points in the instruction book.
Sounds pretty simple so far, but please let me offer some advice. If you did, then you missed a few steps in the previous startup procedure. Pumps are expensive, and you can easily waste all of the cost and more in the one second it takes to push the start button. Another troublesome issue I frequently observe is that the person with the least amount of operating experience is selected as the supervisor for the startup. The person is selected for several reasons, which are unofficial but nevertheless realistic, including: the startup is on third shift or a weekend or a holiday; the building is not heated; the building is not cooled; there is no building and the weather is miserable; the site is remote; and finally, the fatal assumption that a formal education means you surely had a class on pump startup somewhere in the past.
The more complicated the pump and the system, the more steps and checks required. I will not cover more sophisticated installations and procedures, because these operators typically have extensive training and experience.
Examples of these basics that should have been done earlier are foundation design, grouting, elimination of pipe strain, ensuring sufficient net positive suction head NPSH margin, pipe size and system geometry, materials choices, system hydro test, system instrumentation, submergence calculations and auxiliary systems. Consequently, I will address a few things that are important for this group. ANSI pumps include adjustable impeller clearance settings.
There are basically two styles that are the opposite of each other, but regardless of the style they must be adjusted to the proper clearance prior to startup. The mechanical seal will also need to be adjusted and set. For this reason, these pumps are typically shipped without the coupling installed. It is essential to perform the driver rotation check prior to the coupling installation.
Skipping this step is unfortunately a common problem. Often misunderstood, or simply overlooked, the pump must be primed prior to startup. Even a self-priming pump must be primed the first time.
The brief definition of primed means that all the air and noncondensable gases are removed from the pump and suction line and that only liquid is present in the system. If the pump is in a flooded system, the process of priming is easy. A flooded system simply means that the source of liquid is at an elevation above the pump impeller centerline—gravity is your friend in the priming process. To remove the air and noncondensable gases, you still must vent them outside of the system.
Most systems will include a vent line with a valve or a removable plug to facilitate this. Oil-less pumps, however, are cleaner, require less monitoring and maintenance, and easily generate vacuums in a range useful for vacuum bagging. Of the several types of positive displacement vacuum pumps useful for vacuum bagging, the reciprocating piston type and the rotary vane type are most common. Piston pumps are able to generate higher vacuums than rotary vane pumps, accompanied by higher noise levels and vibration.
Rotary vane pumps may generate lower vacuums than piston pumps, but they offer several advantages. While their vacuum ratings are more than adequate for most vacuum bagging, they are able to move more air for a given vacuum rating. In other words, they can remove air from the system faster and tolerate more leaks in the system while maintaining a useful vacuum level. In addition, rotary vane pumps are generally more compact, run more smoothly, require less power, and cost less.
Non-positive displacement vacuum pumps have high CFM cubic feet per minute ratings, but generally at vacuum levels too low for most vacuum bagging. A vacuum cleaner is an example of a non-positive displacement or turbine type pump. Air-operated vacuum generators are simple, low-cost Venturi devices that generate a vacuum using air pressure supplied by a standard air compressor. Their portability, relatively low cost and the accessibility of compressors in many shops and homes make Venturi generators ideal for smaller vacuum bagging projects.
Single-stage generators have a high vacuum rating, but move a low volume of air, limiting the size of the vacuum bagging operation. Larger two-stage pumps are comparable to mechanical pumps for most vacuum bagging operations, but require a proportionately larger compressor to run them.
Whichever vacuum generator you choose, it must hold a continuous vacuum until the epoxy reaches an effective cure. This may take 8 to 24 hours depending on the hardener selected and ambient temperature. After all the materials are in place, turn on the vacuum source and allow vacuum to be continually pulled until the epoxy has cured.
What is vacuum bagging? Why vacuum bag a laminate? What materials do I need for vacuum bagging and how do I use them? Sealant tape Lay down a layer of sealant tape around the perimeter of the part, leaving some space between it and the laminate. Release fabric Release fabric should be laid directly on top of the wet laminate. Release film Perforated release film is a thin plastic with small holes that control how the excess epoxy moves from the part to the breather fabric. Breather fabric The function of the breather fabric is really two-fold.
The analysis of gases at low pressures is not only useful when analysing residual gases from a vacuum pump, leak testing at a flange connection, but also for vacuum supply lines. They are also essential in the broader fields of vacuum technology applications and processes. Partial pressure is that exerted by a particular gas within a mixture of gases. The total of all partial pressures gases present, gives the total.
The distinction among the various types of gases is essentially on the basis of their molar masses. The primary purpose of analysis is therefore to register qualitatively the proportions of gas within a system and determine quantitatively the amount of each gas. The measurement cell is a hot cathode ionization vacuum gauge.
Electrons are emitted from the hot filaments and accelerated toward the source via an electrical bias. The fast moving electrons collide with the gas molecules, dislodging electrons, thus ionizing them. Positive gas ions provide their current to the negative loaded ion collector. Ion current is proportional to pressure: The more ions, the higher the ion current.
The quadrupole array is composed of four stainless steel rods. This creates a complex magnetic field and by varying the voltage the magnetic field is controlled.
Want to learn more about how vacuum science is utilised in different applications? Learn how research and development such as nuclear fusion, space and medical research as well as different analytical instruments are able to operate with the help of vacuum technology. Privacy Policy. English Italiano. The Fundamentals of Vacuum Science.
Table of Contents. Vacuum Physics - Basic Terms. Pressure Units What is the unit of Vacuum Pressure? Below is an overview of the major pressure units and conversion of pressure units: Vacuum Ranges It is common in vacuum science to sub-divide pressure ranges into five individual regimes: Rough or Low vacuum R : Atmospheric to 1 m b ar Medium or Fine vacuum MV : 1 to 10 —3 m b ar High vacuum HV : 10 —3 to 10 —7 m b ar Ultra-high vacuum UHV : 10 —7 to 10 —1 2 m b ar Extreme High Vacuum XHV : greater than 10 m b ar.
Flow types Vacuum technology is usually associated with three types of flow: viscous or continuum flow; molecular flow; and a transitional range between these two known as Knudsen flow. Conductance All fixtures between intake of pump system and chamber will lead to a reduction of pumping speed.
Vacuum Generation. If p and V are constant at the intake side of the pump, the throughput of this pump can be expressed with the simple equation where S is the pumping speed of the pump at intake pressure of p. Ultimate pressure Ultimate pressure p ult is the lowest pressure of a blank-flanged vacuum pump under defined conditions without gas inlet. Pump classification The correct choice and usage of a vacuum pump is essential.
Pump Selection In order to ensure a proper pump selection for a vacuum application several points need to be considered, such as: Pump fit for the vacuum system performance, installation, operation, control, Safety and regulatory requirements Click here to find out more about the criteria you should consider to select the right pump in our eBook.
Vacuum Measurement. Measurement principles The physical properties of gases change with pressure. Vacuum Gauge Types Table of Technologies and their standard measuring ranges Piezo - Works on the principle that under a mechanical load, Semiconducting materials experience a change in their resistivity.
Its most common form is the Inverted Magnetron , although Penning type gauges are also widely used in some applications Active vs Passive Generally, vacuum gauges fall into two categories: active and passive.
Leak Detection. When searching for leaks one will generally have to distinguish between two tasks: Locating leaks and Measuring the leak rate In addition, we distinguish, based on the direction of flow for the fluid, between the a. When measuring leak rates we differentiate between registering individual leaks local measurement the total of all leaks in the test specimen integral measurement. These are: the mass spectrometer the high vacuum pump and the auxiliary roughing pump system in stationary units.
Gas Analysis. An RGA consists of the sensor, the interface box and the control unit. The sensor must be exposed to vacuum as it requires low pressures to start working.
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