Strainers performance

Pressure gauges should always be fitted on the discharge side of liquid pumps, to check performance and give warning of a possible drop in flow resulting from dirty strainers. Manometer pressure gauges are required across air filters (see Chapter 2 7). 

This interaction depends on stock temperature and in turn on the performance of PVC melts. Flexible PVC is normally calendered at temperatures of 10 to 20C (50 to 68F) lower than rigid PVC. In flexible PVC production, a short single screw extruder acting as a strainer filters out contaminants from stock before reaching the calender. This important method is not applicable to rigid PVC because it drastically increases the head pressure and the consequent overheating would cause the stock to decompose. 

Melanosis, leukosis, and xanthosis alchemy procedures were performed in a device called a kerotakis. Figure 1.1 shows how a kerotakis might have looked. In the kerotakis, a metal sample like copper was placed on a screen in a tall container. Sulfur was added and the entire container heated by a small fire in the base. When the sulfur was hot, it acted on the metal. Condensing sulfur-containing sulfides settled out. A sieve, like a spaghetti strainer only flat, held back pieces of unreacted metal, while a black compound collected at the kerotakis bottom. This mixture was heated in an open container to remove any extra sulfur. 

Process technicians use hydraulic systems (see Figure 9-6) to open or close valves, lift heavy objects, run hydraulic motors, and stop the rotation of a rotary or reciprocating device. A hydraulic system is a collection of equipment designed to apply pressure on a confined liquid in order to perform work. A similar process is used in the brake systems of most cars and trucks. A hydraulic system is composed of a fluid reservoir, strainer, pump, piping, flow control valve, pressure control valve, four-way directional control valve, and actuator (cylinder, piston). 

A feed pump transfers the product to the atomizer either directly or via a constant-head feed tank. The feed tanks are of sufficient volume to permit continuous operation and to smooth out possible interruptions and variations in the supply of the material. It is quite usual for two holding tanks to be used alternately, thus assuring constant product supply to the dryer. The feed strainer or filter is important because all matter likely to jeopardize the performance of the dryer through partial or total blockage of the atomizer must be removed. Demineralized water or clean condensate is usually required for use in cases of feed blockage. 

Perforated metal sheets are more rigid and can be made stronger than woven wire cloths and so they find particular applications in strainers, coarse filters and screens. Perforated metal strainers have a predictable and consistent performance because the size of the screen openings is controlled in the manufacturing process. 

Screens, screening machines and rotary strainers can trap solid particles down to about 15 om, have high capacities and are relatively inexpensive. Conventional filters can also perform a similar duty on low volume systems and are produced in a variety of forms to fit in both centralized and individual systems. They may also be used with, or combined with, magnetic filters to separate and retain ferrous metal particles. 

Earlier industrial hydraulic systems operated at pressures of 100 bar or less, and usually performed satisfactorily with minimal attention to filtering. Often a simple strainer on the pump discharge, or a filter with a cut-off of 25 to 50 pm, provided adequate protection. Some systems, in fact, dispensed with a filter entirely, instead withdrawing oil periodically for batch filtration and return to the system. 

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