Pumps, piston-type

For small feed rates, it may be considerably cheaper to use a positive-displacement pump (piston type). Control may be by stroke adjustment on a constant-speed pump as shown by Figure 5.2A or by adjustment of a variable-speed drive of a pump with a fixed stroke as shown by Figure 5.2B. If the minimum stroke rate is at least three times the reciprocal of the feed-tray holdup time, no pulsation damper is required. 

Reciprocating pumps are those most commonly used in high performance Ic. The single-piston type usually has inlet and outlet check valves with some mechanism such as variable stroke frequency to minimize the effect of pump pulsations. Dual-piston pumps operate with the pistons 180° out of phase to minimize pulsations. For this system to work optimally, the piston units must be identical. 

Calibrate the detector tube pump for proper volume measurement at least quarterly. Simply connect the pump directly to the bubble meter with a detector mbe in-line. Use a detector mbe and pump from the same manufacturer. Wet the inside of the 100 cc bubble meter with soap solution. For volume calibration, experiment to get the soap bubble even with the zero ml mark of the buret. For piston-type pumps, pull the pump handle all the way out (full pump stroke) and note where the soap bubble stops for bellows-type pumps, compress the bellows fully for automatic pumps, program the pump to take a full pump stroke. 

As the flow rate and quantity of liquor are the most important controllable variables in developing design data, a feed pump suitable for accurate and continuous flow is required. Depending on the size of the pilot column system, the use of peristaltic, diaphragm, piston-type or centrifugal pumps are recommended. The feed pump should be used in combination with a volumetric or gravimetric flow control... 

With the exception of piston-type pumps, most of the common positive-displacement pumps utilize rotating elements to provide a constant-volume, constant-pressure output. As a result, these pumps can be monitored with the following parameters hydraulic instability, passing frequencies, and running speed. 

With the exception of piston-type pumps, all positive-displacement pumps have one or more passing frequencies generated by the gears, lobes, vanes, or wobble-plates... 

This pump is the same in principle as the piston type but differs in that the gland is at one end of the cylinder making its replacement easier than with the standard piston type. The sealing of piston and ram pumps has been much improved but, because of the nature of the fluids frequently used, care in selecting and maintaining the seal is very important. The piston or ram pump may be used for injections of small quantities of inhibitors to polymerisation units or of corrosion inhibitors to high pressure systems, and also for boiler feed water applications. 

Vacuum pumps reciprocating piston type decrease the pressure to 1 Torr rotary piston down to 0.001 Torr, two-iobe rotary down to 0.0001 Torr steam jet ejectors, one stage down to 100 Torr, three stage down to 1 Torr, five stage down to 0.05 Torr. 

Liquid-Piston Type This type is illustrated in Fig. 10-97. These compressors are offered as single-stage units for pressure differentials up to about 0.52 MPa (75 Ibf/in ) in the smaller sizes and capacities up to 6.8 X 10 mVh (4000 fF/min) when used with a lower pressure differential. Staging is employed for higher pressure differentials. These units have found wide application as vacuum pumps on wet-vacuum service. Inlet and discharge ports are located in the impeller hub. As the vaned impeller rotates, centrifugal force drives the sealing liquid... 

Type of pump Reciprocating, piston-type metering pump... 

Notes All water cooled exchangers operate with water in at 75°F and out at 100°F. All pumps are centrifugal except the complex transfer, and the sulfonation reactor feed, which are both piston type the neutralization reactor recirculation pump and the transfer pumps are gear pumps. 

Piston Type of Mechanical Vacuum Pump, Vacuum, 19, 17-22 (1969). 

The feed pump was a positive-displacement, piston-type metering pump. All liquid transfer lines in the system were traced with electric resistance heaters which allowed us to process heavy SRC solutions. 

A piston-type transfer cylinder is used for the injection of fluid into the model through a type-304 stainless steel transfer cylinder, 800 cc, manufactured by Welker Engineering Company. The cylinder is located inside the temperature chamber to equilibrate the contents to the test temperature prior to injection. Fluid is injected into the model by pumping hydraulic oil into the transfer cylinder. Mixing of the hydraulic oil with the injection fluid is eliminated by a sliding piston built into the cylinder. 

Reciprocating piston pumps. Around 85% of the HPLC pumps in current use are of the reciprocating piston type. Figure 5.2 shows a basic representation of their construction. With this type of pump, the mobile... 

As stated above, it is highly desirable that the flow generated by a pump should be practically free from pulsations. Pulsations in flowrate can reduce the sensitivity of a method, and in extreme cases, damage the column. The most commonly used class of analytical HPLC pump, the reciprocating piston type, inherently provides relatively constant flow -particularly when multiple pistons are used. However, the current drive towards the detection of smaller and smaller quantities means that levels of pulsation that were perfectly acceptable only a few years ago are now regarded as unsuitable for many applications. The minimisation or eradication of pump pulsation may be achieved by mechanical or electronic means, or by a combination of the two. 

---