Putting a Stop to the Stop-and-Go
[2008-7-29]
Tag : Blood Pressure Meter
One way to smooth the flow is to use a double-acting pump or onewith multiple pistons. Since each piston stroke reaches its maximumat a different time, this smoothes out the pressure highs and lowsthe same way a 12-cylinder Jaguar engine runs much smoother than asingle piston lawnmower. The K Factor of a pump is a figure showinghow much the flow volume varies from the average flow volume atdifferent points of the piston stroke. A simplex, single-actingpump has a K Factor of 0.60, meaning the fluid volume at thedischarge port varies 60 percent above and below the average flow.Adding more pistons lowers the K Factor to the point where, withseven pistons, the K Factor drops to only 0.02. Of course, not manyseptuplex pumps are in use. The more typical simplex, duplex andtriplex pumps require pulsation dampeners to bring their pulsationproblems under control.
Smooth Strokes
Pulsation dampeners are devices attached to the pump output thatmoderate the pump’s pressure and volume fluctuations. Theycan be attached on a nipple off the outlet line, or they can sit inline. Numerous designs are available, but the basic elementsconsist of a sphere containing a diaphragm or a cylinder containinga bladder. With the first design, the diaphragm is held in place bythe two halves of the sphere. The diaphragm splits the interior ofthe sphere into two halves, one containing nitrogen and the othercontaining the fluid being pumped. A charging valve and a pressuremeter sit on the gas side of the sphere. The other side connects tothe plumbing. The cylindrical design is similar in operation, but abladder is attached to the charging valve and the fluid flows inaround the bladder.
In both cases, the gas side of the dampener is precharged to about80 percent of the minimum allowable system pressure, so there willalways be some liquid within the dampener. Because the nitrogen ismore compressible than the hydraulic fluid, when the fluid ispressurized most of the fluid above the average system flow goesinto the pulsation dampener, rather than creating a compressionwave. Then, during the low pressure portion of the piston stroke,the gas expands to force the fluid back out of the dampener intothe system, maintaining the mean flow and pressure.
One way to smooth the flow is to use a double-acting pump or onewith multiple pistons. Since each piston stroke reaches its maximumat a different time, this smoothes out the pressure highs and lowsthe same way a 12-cylinder Jaguar engine runs much smoother than asingle piston lawnmower. The K Factor of a pump is a figure showinghow much the flow volume varies from the average flow volume atdifferent points of the piston stroke. A simplex, single-actingpump has a K Factor of 0.60, meaning the fluid volume at thedischarge port varies 60 percent above and below the average flow.Adding more pistons lowers the K Factor to the point where, withseven pistons, the K Factor drops to only 0.02. Of course, not manyseptuplex pumps are in use. The more typical simplex, duplex andtriplex pumps require pulsation dampeners to bring their pulsationproblems under control.
Smooth Strokes
Pulsation dampeners are devices attached to the pump output thatmoderate the pump’s pressure and volume fluctuations. Theycan be attached on a nipple off the outlet line, or they can sit inline. Numerous designs are available, but the basic elementsconsist of a sphere containing a diaphragm or a cylinder containinga bladder. With the first design, the diaphragm is held in place bythe two halves of the sphere. The diaphragm splits the interior ofthe sphere into two halves, one containing nitrogen and the othercontaining the fluid being pumped. A charging valve and a pressuremeter sit on the gas side of the sphere. The other side connects tothe plumbing. The cylindrical design is similar in operation, but abladder is attached to the charging valve and the fluid flows inaround the bladder.
In both cases, the gas side of the dampener is precharged to about80 percent of the minimum allowable system pressure, so there willalways be some liquid within the dampener. Because the nitrogen ismore compressible than the hydraulic fluid, when the fluid ispressurized most of the fluid above the average system flow goesinto the pulsation dampener, rather than creating a compressionwave. Then, during the low pressure portion of the piston stroke,the gas expands to force the fluid back out of the dampener intothe system, maintaining the mean flow and pressure.
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