Pressure drop across pumps

A P = pressure drop across pump (N m 2) rj = pump efficiency (—)... 

OTHER LOSSES (SUCTION - e.g. STRAINER/FILTER), psi PRESSURE DROP ACROSS PUMP, pSi. 

Cavitation. The subject of cavitation in pumps is of great importance. When the Hquid static pressure is reduced below its vapor pressure, vaporization takes place. This may happen because (/) the main stream fluid velocity is too high, so that static pressure becomes lower than vapor pressure (2) localized velocity increases and static pressure drops on account of vane curvature effect, especially near the inlets (J) pressure drops across the valve or is reduced by friction in front of the pump or (4) temperature increases, giving a corresponding vapor pressure increase. 

Vacuum pump capacity is conventionally based on the total cycle and expressed as mVh-m" (cfi7i/ft ) of filter area measured at pump inlet conditions. Thus, the gas volumes per unit area passing during each dry period in the cycle are totaled and divided by the cycle time to arrive at the design air rate. Since air rate measurements in the test program are based on pressure drop across the cake and filter medium only, allowance must be made For additional expansion due to pressure drop within the filter and auxiliary piping system in arriving at vacuum pump inlet conditions. 

API mandates that the pressure drop across a clean filter element be no more than 15% of the allowable pressure drop when dirty. An upper limit of 5 psi drop is set for clean filters. This is a reasonable criterion. If a little arithmetic is performed, the head rise for a centrifugal pump may be calculated. The specifications on both of these items must be coordinated and made compatible. 

Equation (11) shows that the pressure drop across the connecting tube increases inversely as the fourth power of the tube radius. It follows that, as it is impractical to dissipate a significant amount of the available pump pressure across a connecting tubing, there will be a limit to the reduction of (r) to minimize tube dispersion. 

The precision rotameter is a secondary calibration device. If it is to be used in place of a primary device such as a bubble meter, care must be taken to ensure that any introduced error will be minimal and noted. The precision rotameter may be used for calibrating the personal sampling pump in lieu of a bubble meter provided it is (a) Calibrated with an electronic bubble meter or a bubble meter, (b) Disassembled, cleaned as necessary, and recalibrated. It should be used with care to avoid dirt and dust contamination which may affect the flow, (c) Not used at substantially different temperature and/or pressure from those conditions present when the rotameter was calibrated against the primary source, (d) Used such that pressure drop across it is minimal. If altitude or temperature at the sampling site are substantially different from the calibration site, it is necessary to calibrate the precision rotameter at the sampling site where the same conditions are present. 

A low-pressure-drop liquid cyclone is sometimes used to clarify liquor discharged from the evaporator. The driving force is the pressure drop across the circulating pump. Thickened slurry is returned through a wide-open cyclone underflow connection to the circulating piping before the pump suction. 

Self-induced spray wet collectors This is the most common type, and relies on its separating action by the induced air from the fan pulling the contaminated air through a curtain of water. It is simple in operation with no pumps or moving parts except for the fan, which is set on the clean side of the collector. The scrubbing action is dependent on the pressure drop across the collector. When set, this is constant and is determined by the water level within the collector. The removal of sludge is either by automatic ejection or manual drag-out. 

Determine the operating point on the pump characteristic curve when the flow is such that the pressure drop across the control valve is 35 kN/m2. 

The pressure drop across the pump is calculated using the following equation ... 

The core - flood apparatus is illustrated in Figure 1. The system consists of two positive displacement pumps with their respective metering controls which are connected through 1/8 inch stainless steel tubing to a cross joint and subsequently to the inlet end of a coreholder 35 cm. long and 4 cm. in diameter. Online filters of 7 im size were used to filter the polymer and brine solutions. A bypass line was used to inject a slug of surfactant solution. Two Validyne pressure transducers with appropriate capacity diaphragms are connected to the system. One of these measured differential pressure between the two pressure taps located about one centimeter from either end of the coreholder, and the other recorded the total pressure drop across the core and was directly connected to the inlet line. A two - channel linear strip chart recorder provided a continuous trace of the pressures. An automatic fraction collector was used to collect the effluent fluids. 

A microparticulate hplc column is a very efficient filter, and if the mobile phase contains any particulate matter, or acquires it from the pump and/or the injection valve due to wear, it will collect at the top of the column. If this happens, the pressure drop across the column for a given flow will gradually increase, and the column may eventually become completely blocked. To prevent this happening, the mobile phase should always be filtered before use, preferably through a 0.5 p,m porosity filter, and guard and scavenger columns should be used as a matter of routine (see Section 5.3.2). 

Gasoline is pumped through a 2 in. sch 40 pipeline upward into an elevated storage tank at 60°F. An orifice meter is mounted in a vertical section of the line, which uses a DP cell with a maximum range of 10in.H2O to measure the pressure drop across the orifice at radius taps. If the maximum flow rate expected in the line is 10 gpm, what size orifice should you use If a water manometer with a maximum reading of 10 in. is used instead of the DP cell, what would the required orifice diameter be ... 

A packed bed that consists of the same medium as that in Problem 3 is to be used to filter solids from an aqueous slurry. To determine the filter properties, you test a small section of the bed, which is 6 in. in diameter and 6 in. deep, in the lab. When the slurry is pumped through this test model at a constant flow rate of 30 gpm, the pressure drop across the bed rises to 2 psia in 10 min. How long will it take to filter 100,000 gal of water from the slurry in a full-sized bed... 

Settling slurries cannot be pumped in laminar flow. Turbulence must exist to prevent the solid particles from settling. Settling slurries should be pumped through pipelines at velocities which just prevent the solid particles from settling. This results in the minimum pressure drop across the pipeline. 

The higher flow rate might also reduce the head that the centrifugal pump produces if we are out on the pump curve where head is dropping rapidly with throughput. For simplicity, let us assume that the pump curve is flat. This means that the total pressure drop across the heat exchanger and the control valve is constant. Therefore, the pressure drop over the control valve must decrease as the the pressure drop over the heat exchanger increases. 

Liquid (sp gr = 1) is pumped from a tank at atmospheric pressure through a heat exchanger and a control valve into a process vessel held at 100 psig pressure. The system is designed for a maximum flow rate of 400 gpm. At this maximum flow rate the pressure drop across the heat exchanger is 50 psi. 

Details of the SEC/Viscometer detector system have been described previously.(16) The key component of the viscometer detector is a differential pressure transducer (CELESCO Model P-7D, Canoga Park, CA) with a jf25 psi pressure range. The transducer monitors the pressure drop across a section of stainless steel capillary tubing (length 2 ft., I.D. = 0.007 in.). Pump pressure fluctuations... 

A glass tube (6-mm I.D. by 8-mm O.D. by 3-cm long) is packed with approximately 100 mg of sorbent in a front section and 50 mg in a backup section, each separated by glass wool plugs. Sorbents of coarse mesh size ( 20/40) are used to minimize the pressure drop across the tube. A calibrated personal sampling pump draws air through the sorbent tube at a flow rate of up to 1 liter/min. 

All HPLC systems include one or several pumps that are used to flow the mobile phase through the packing, which is fairly compact and responsible for a pressure drop across the column that can be as high as 20 000 kPa. This elevated pressure, created before the injector, depends on the flow rate, the viscosity of the mobile phase and the size of the particles that form the stationary phase. The pumps are metered in order to maintain a stable flow and avoid pulsations even when the composition of the mobile phase varies. 

When the control valve downstream of a pump is operating in a mostly closed position, the upstream pump is a good candidate to have its impeller trimmed. Sometimes, the pressure drop across a control valve is so huge (>100 psi) that it makes a roaring sound. The energy represented by this wasteful AP is coming from the electricity supplied to the pump s motor. Hence, trimming the impeller also reduces wear because of erosion in downstream control valves. 

In prepared catalysts the pore sizes may be quite uniform. However, in most naturally occurring materials there is a wide range of pore sizes. The actual pore size distribution can be obtained from methods such as porosimetry, in which a nonwetting liquid (usually mercury) is pumped into a solid sample [12,13,15,26,30,55]. The solid is considered to be composed of a bundle of capillaries. For each capillary, the Laplace equation (see Section 3.2.2) gives the pressure drop across a curved liquid surface ... 

So far we have neglected the effect of the flight clearance. As small as the clearance is, polymer melt is being dragged across the clearance by the barrel surface and the pressure drop may pump melt across the flight width. This creates a continuous leakage flow from downstream locations to (one turn back) upstream locations, reducing net flow rate. 

One important recommendation to remember is that extra increments of pumps are started by pressure but stopped on flow. The pump speed is set to keep the pressure drop across the lowest user above some minimum limit. If the header supply pressure instead of the pressure drop across the load is to be controlled, the pressure transmitters should be located on main raisers or headers and should not be near major on-off loads. 

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