Spring pumps

Engineering thermoplastics possess better dynamic mechanical properties than other thermoplastics. They have current or potential apphca-tions for gears, valves, rotating blades, biomechanicals such as prosthetics and orthopedic implants, springs, pumps, thin film membranes, transmission components, and small-amphtude vibration step-loading apph-cations [3]. 

Electrohvdraiilic actuators have similar performance characteristics and cost/rnaintenance ramifications. The main difference is that they contain their own electric-powdered hvdraiilic pump. The pump rnav rim continuously or be switched on when a change in position is required. Their main application is remote sites without an air supply when a failsafe spring return is needed. 

This type of seal has the rotary component and face mounted outside the seal chamber. The springs and drive elements are outside the pumped liquid. This reduces the problems associated with corrosion and the accumulation of pumped product clogging the springs. This seal is popular in the food processing industry. The pumped liquid arrives to the inside diameter of the faces and seals toward the outside diameter. The environment outside the pump approaches the OD of the face union. Pressures are limited to about 35 psig. Sometimes this. seal can be mounted either inside or outside the pump. This seal is easy to install, adjust, and maintain. It permits easy access and cleaning of the pump internal parts, often required in the food processing industry. 

Extremely High Velocity Shaft Speed Some pump companies use very high velocity, 30,000 rpm, to improve efficiency and generate high head with small equipment. U.se a stationary seal, with the springs in the stationary element. 

This dial indicator is fixed to the volute mounting adapter collar of the pump and the needle is on the shaft (Figure 14-21). The shaft should be moved radially by hand (see the arrows) up and down. Note the movement in the indicator. This is a check of the radial tolerance in the bearing. Some people use the word run out . Radial dellection causes misalignment of the rotating and stationary faces of the mechanical seal. This shortens the seal life by eausing drive pins and springs to wear and rub in relative motion. 

Normal procedure would be to specify the pump PR valve differential spring... 

The natural frequency, co associated with the mode shape that exhibits a large displacement of the pump is compared with the fundamental frequency, of the wall. If co is much less than ru, then the dynamic interaction between the wall and the loop may be neglected, but the kinematic constraint on the pump imposed by the lateral bracing is retained. If nearly equals nr , the wall and steam supply systems are dynamically coupled. In which case it may be sufficient to model the wall as a one-mass system such that the fundamental frequency, Wo is retained. The mathematical model of the piping systems should be capable of revealing the response to the anticipated ground motion (dominantly translational). The mathematics necessary to analyze the damped spring mass. system become quite formidable, and the reader is referred to Berkowitz (1969),... 

When the system pressure decreases to a point slightly below 600 psi, the spring forces the piston down and closes the pilot valve. When the pilot valve is closed, the fluid cannot flow directly to the return line. This causes the pressure to increase in the line between the pump and the regulator. This pressure opens the check valve, causing fluid to enter the system. 

As the pump shaft rotates, the shaft packing rotates with it due to friction. (In more complex mechanical seals, the shaft-packing element is secured to the rotating shaft by Allen screws.) There is also friction between the spring. 

The other drawback is simply one of economics. Because pumps come in a variety of shaft sizes and speeds, the use of this type of seal requires inventorying several sizes of spare springs, which ties up capital. 

Nevertheless, the simple and reliable coil spring seal has proven itself in the pumping industry and is often selected for use despite its drawbacks. In regulated industries, this type of seal design far exceeds the capabilities of a compressed packing ring seal. 

As an example plastic replaced a metal pump in a PVC plastic bag containing blood. The plastic spring hand-operating pump did not contaminate the blood. 

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