API STD 681-2010 pdf download.Liquid Ring Vacuum Pumps and Compressors for Petroleum, Chemical, and Gas Industry Services.
1.1 Scope 1.1.1 This standard covers the minimum requirements for liquid ring vacuum pump and compressor systems for service in the petroleum, chemical, and gas industries. This includes both vacuum pump and compressor design and system design. 1.1.2 The design of the system is critical to the successful operation of the liquid ring vacuum pump or compressor. Close attention must be paid not only to the design of the ring liquid system but also to how it is integrated into the user’s process. 1.1.3 Although this standard covers minimum require- ments appropriate for petroleum refinery service, purchasers may wish to consider pumps, compressors, and systems that do not meet all the requirements of this standard, based on specific nonfammable, nontoxic service conditions. Note: A bullet (●) at the beginning of a paragraph indicates that a decision by the purchaser Is required. These decisions should be indicated on the data sheet (see Appendix A); otherwise, they should be stated in the quotation request or In the order. 1.2 Alternative Designs The vendor may offer alternative designs. Equivalent metric dimensions, fasteners, and fanges may be substituted as mutually agreed upon by the purchaser and the vendor. 1.3 Conflicting Requirements In case of conflict between this standard and the inquiry, or order, the information included in the order shall govern. 1.4 Definition ofTerms Terms used in this standard are defincd in 1.4.1 through 1.4.26 (refer to Figure 1).
1.4.4 Inlet cubic feet per minute (ICFM) refers to the flow rate determined at the conditions of pressure, temperature, compressibility, and gas composition, including moisture, at the compressor inlet flange. Actual cubic feet per minute (ACFM) may be used to refer to flow at a number of locations and should therefore not be used interchangeably with inlet cubic feet per minute. 1.4.5 A liquid ring vacuum pump, or compressor, is a rotary positive-displacement machine in which gas compres- sion is achieved by the action of a radially bladed impeller mounted in an eccentric or lliptical casing which is partially filled with liquid. 1.4.6 Maximum allowable differential pressure is the maximum differential pressure for which the manufacturer has designed the equipment for continuous operation. 1.4.7 Maximum allowable speed (revolutions per minute) is the highest speed at which the manufacturer s design will permit continuous operation. 1.4.8 Maximum allowable temperature is the maximum continuous temperature for which the manufacturer has designed the equipment (or any part to which the term is referred) when handing the specified fluid at the specified pressure. 1.4.9 Maximum allowable vacuum is the maximum vacuum (minimum suction pressure) for which the manufacturer has designed the equipment, corrected for the vapor pressure of the seal liquid at the operating temperature. . 1.4.10 Maximum allowable working pressure is the maximum continuous pressure for which the manufacturer has designed the equipment (or any part to which the term is referred) when handling the specifed fuid at the specified temperature.
1.4.13 Maximum discharge pressure is the maximum suction pressure plus the maximum dfferential pessure that the pump is able to develop when operating at the specified speed, specific gravity, and pumping temperature. 1.4.14 Maximum sealing pressure is the highest pressure expected at the seals during any specified static or operating condition and during start-up and shutdown. 1.4.15 Minimum allowable temperature is the minimum continuous temperature for which the manufacturer has designed the equipment (or any part to which the term is referred). 1.4.16 Normal operating point is the point at which usual operation is expected and optimum eficiency is desired. 1.4.17 The casing is the composite of all stationary pres- sure-containing parts of the unit, including all nozzles, seal glands, and other attached parts but excluding the stationary and rotating members of mechanical seals (see Figure E-1, Appendix E). 1.4.18 Radially split refers to casing joints that are transverse to the shaft centerline. 1.4.19 Rated discharge pressure is the highest pressure required to meet the conditions specifed by the purchaser for the intended service. 1.4.20 The rated operating point is the point al which the vendor certifies that performance is within the tolerances stated in this standard. Performance includes the following factors: capacity, power, eficiency, rotative speed, and rated suction and discharge pressures.