tailieunhanh - Improving Machinery Reliability 3 Episode 5

Tham khảo tài liệu 'improving machinery reliability 3 episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 154 improving Machinery Reliability Figure 3-45. Comparison of the effect of three pump casing designs on radial force. Courtesy Pump World Vol. 2 No. 1 1976. contention that competent correlation research on these parameters is highly desirable. Consideration of an additional parameter shaft deflection is intuitively evident to the mechanical engineer who visualizes overhung impeller construction of centrifugal pumps as essentially a cantilevered beam with the concentrated load . unbalanced fluid force p acting at the free end and producing a maximum deflection of PL1 2 3 3E1 . With Young s modulus E a constant shaft deflection can be reduced by selecting pumps with a low ratio of L3 where L - overhung distance impeller to nearest bearing and I shaft area moment of inertia a function of the shaft diameter D raised to the fourth power. All of this can be translated to read For a given casing design overhung impeller centrifugal pumps with low L3 D4 5 6 values will undergo less shaft deflection than pumps with high L3 D4 values. Choosing ANSI API Back-Pullout or Between-Bearing Pumps. To the best of our knowledge there are no firm rules or regulations defining when it would be either appropriate or necessary to use a particular pump geometry or style. However on the issue of ANSI vs. API pumps we can at least offer rules-of-thumb that are shared by many HP reliability professionals. For toxic flammable or explosion-prone services especially at onsite locations in close proximity to furnaces and boilers a large number of reliability-minded machinery engineers would use API-610 8th Edition pumps if one or more of the following were to exist 1. Head exceeds 350 ft 2. Temperature of pumpage exceeds 300 F 149 C on pumps with discharge flange sizes larger than 4 in. or 35O F 177 C on pumps with 4-in. discharge flange size or less 3. Driver horsepower exceeds 100 hp 74 kW 4. Suction pressure in excess of 75 psig 516 kpa 5. Rated flow exceeds flow at best .