Pump Type Follows:

Tuesday, June 30, 2009

The Design of Packing Rings

Packing is used in the stuffing box of a centrifugal pump to control the leakage of the pumped liquid out, or the leakage of air in, where the shaft passes through the casing. The basic form of a seal can be applied in light-to medium duty services and to those liquids that prove to difficult to mechanic seals.

Packing may be referred to as compression, automatic or floating. Each term describes the type of operation in which the packing will be used.

Automatic and floating packing require no gland adjustment in controlling leakage. Automatic packing are confine to a given space and are activated by the operating pressure. Automatic packing rings are designed in the form of V-rings, U-cups and O-rings. Floating packing include piston rings and segmental rings that may be energize by a spring. These type of packing are commonly used in reciprocating application.

Compression packing is most commonly used on rotating equipment. The seal is formed by the packing being squeeze between the inboard end of the stuffing box and the gland. A static seal is formed at the end of the packing ring and at the inside diameter of the stuffing box. The dynamic seal is formed between the packing and shaft or shaft sleeve. Under a load, the packing deforms down against the shaft, controlling leakage. Some leakage along the shaft is necessary too cool and lubricate the packing. The amount of leakage will depend on the materials of the construction for the packing, the operating condition of the application, and the condition of the equipments.

Packing must be able to withstand equipment variables. The design of the packing ring and the materials of construction must be resilient to follow shaft run out and misalignment, as well as to compensate for thermal growth of the equipment without an appreciable increase in leakage.

Wednesday, June 3, 2009

Sealless Pumps

Completely leakproff pumps are available for pumping corrosive, volatile, radioactive and otherwise hazardous liquids. Canned motor pumps are an assembly of a standard centrifugal pump and a squired cage induction motor in a hermetically sealed unit. Modifying a recalculating flow system in a canned motor pumped can allow it to be used in applications at up to 1000 oF (638 oC).

Magnetic drive pumps are an assembly of a rotor, an impeller, product lubricated bearings and a magnetic carrier inside an isolation shell or diaphragm. This rotor is driven by magnets outside outside the shell or diaphragm. No mechanical connection exist between the driven magnet and driving magnets. No seal exist and thus we have the term “sealless.”

Straight Radial Vane High Speed Pumps

For handling volatile liquids at low flow rates and high heads, the straight radial vane impeller in a diffuser casing offer several advantages. Volatile low specific gravity, poor lubricity liquids require larger running clearances, which is not possible with conventional high head multistage centrifugal or positive displacement pumps. High head pumping of this liquids can be handled by operating this completely open impeller at very high speeds through an integral gear increaser and with very large impeller to casing clearance, typically 0.030 to 0.070 in (0.76 to 1.8 mm). Test of one manufacturer’s design have shown this clearance can increase t 0/125 in (3.2 mm) with virtually no change in performance, and consequently there is no need to provide adjustment for impeller axial clearance.