All rotating machines, pumps included, vibrate to some extent due to various reasons, the most common of which are typically the following: Improper installation at site Improper balancing of pump rotor Excessively turbulent fluid flow Cavitation or internal recirculation in pumps Normal pump wear after prolonged operation. Therefore, process and design engineers should not be so much interested as to whether or not a pump vibrates but concerned and instead ask themselves the following questions: Is the pump vibration a symptom of some other more worrying phenomena occurring within the pump, like for example - pump cavitation? Pump vibration monitoring instruments Large sized centrifugal pumps are generally recommended to be equipped with typically two 2 vibration measurement instruments per bearing, one at the x-axis and the second at the y-axis. These instruments are typically programmed with two threshold values: an alarm point and a trip point. When the alarm point is reached, operator is notified at the control room in order to take measures to verify and limit the vibration level.
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Standard Consensus is established when, in the judgement of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantialagreement means much more than a simple majority, but not nec- essarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution. The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether he has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes, or proce- dures not conformingto the standards.
The American National Standards Institutedoes not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American NationalStandards Institute. Requests for interpretations should be addressed to the secretariat or sponsor whose name appears on the title page of this standard.
The procedures of the American National Standards Institute require that action betaken periodically to reaffirm, revise, orwithdraw this standard. Purchasersof American National Standards may receive current informationon all standards by call- ing or writing the American National Standards Institute. No partof this publication may be reproducedin any form, in an electronic retrievalsystem or otherwise,without prior written permissionof the publisher.
Purpose of Standards I Hydraulic Institute Standards are adopted in the public interest and are designedto help eliminate misunderstandings betweenthe manufacturer, the purchaserandlor the user and to assist the purchaser in selecting and obtaining the proper product for a particular need.
Existence of Hydraulic InstituteStandards does not in any respect preclude a member from manufacturingor selling products not conforming to the Standards. Questions arising from the con- tent of this Standard may be directed to the Hydraulic Institute.
It will direct all such questions to the appropriate technical committee for provision of a suitable answer. Ifa dispute arises regarding contents of an Institute publicationor an answer pro- vided by the Instituteto a question such as indicated above, the point in question shall be referredto the Executive Committeeof the Hydraulic Institute, which then shall act as a Boardof Appeals. Units of Measurement This standard is written using both metric and US Customary units of measure- ment.
Metric unitsappearfirst followed by US units in brackets. Tables, charts and sample calculations are printedtwice, first in metric units, then in US units. Consensus for this standard was achieved by use of the Canvass Method The following organizations, recognized as having an interest in the standardiza- tion of centrifugal pumps, were contacted prior to the approval of this revision of the standard. Inclusionin this list does not necessarily imply that the organization concurred with the submittal of the proposedstandardto ANSI.
KSB, Inc. BechtelCorporation M. Ortev Enterprises Inc. PattersonPump Company Cuma S. PinellasCounty, Gen. Dean Pump Division, MetproCorp. FairbanksMorse Pump Corp. Constructionand Skidmore Facilities Dept. South Florida Water Mgmt. Illinois Departmentof Transportation Systecon, Inc. Messina Pump and Hydr. Beekman, Floway Pumps FredericW. Other more complex shapes may also occur. Included is a description of the dynamics of vibration, vibration measurement, allowable vibration Figure has the lowest natural frequency and is values and factors that effect vibration.
Figure has a higher natural frequency than Figure and Dynamics of vibration is sometimes called the second critical speed. All centrifugal and vertical turbine pumps have rotors Determination of lateral critical speed is important for and structures that can vibrate in response to excita- pumps and associated rotating equipment because if tion forces. When the frequency of the excitation a critical speed or resonant frequency is close to an forces is close to the natural frequencies of the struc- operating speed or other exciting frequency, such as tures, resonance can occur and excessive and dam- the impeller vane pass frequency, small excitation aging vibration levels can be reached.
These natural forces can be greatly amplified. The resulting stresses frequencies of vibration usually occur in one or more and deflections can cause premature equipment failure. Structure lateral vibration Calculation of critical speed can become very com- plex, depending on the effects one wants to consider in The natural frequencies of vibration can be deter- the calculation. A simple calculation of the first critical mined by one of the following methods: speed of a rotor is done by determining the static deflection of the center of gravity of a shaft or rotor Simple beam formulas based on those derived under its own weight, when assumed to be in a hori- from common structural mechanics zontal position despite its actual orientation.
asni HI 9.6.4
Brad Kelechava Leave a comment Head —the height at which a pump can raise water up vertically through a discharge pipe or tube—is an important factor in determining the overall performance and requirements of a pump. The concept of general pump head is fundamental, but net positive suction head available NPSHA is crucially applicable to rotodynamic pumps. NPSHR is the minimum value designated because it will keep the pump from cavitating, and it is a function of the pump. Therefore, it must be provided by the pump manufacturer. This value was implemented in the industry as early as the s, after it had appeared in published voluntary consensus standards.
Pumps vibrations limits as per international standards