Entry suction pressure

With the progressive removal of the liquid, the curve at first rises almost vertically but subsequently tapers off to acquire a gradual slope. The intersection of the tangents extended from the steep and the flat portions of the curve occurs at about S = 0.9. At this saturation, the capillary pressure is known as entry suction Pe, and the pellet strength attains its maximum (R5). 

Although the capillary pressure curve cannot be predicted from the fundamental properties of the particulate bed, a crude estimate of the entry suction for wetting liquids is given by (N2)... 

A pump lifts water from a lake. At the pump suction entry a foot valve is fitted. Determine the maximum static delivery height the water can be raised without cavitation taking place. The saturation pressure of water is 1.23 kPa at 10 °C and the dynamic viscosity is 1.3 x 10" kg m s T The suction pipe water velocity is 2.0 m s , the internal pipe diameter is 100 mm, and the pipe roughness is 0.03 mm. The resistance of the foot valve is 4.5. 

The regenerative pumps (1) consist of two double-suction impellers, each with a diameter of 0.036 m in series to increase the total pump head. All pumps are equipped with speed control and differential pressure sensors. The mixed phases enter the fluid cyclone (2) of 0.020 m diameter with a tangential tube entry. The underflow of the cyclones is connected to a small storage tank (3) with level con-... 

Another problem with submerged pumps is the amount of chlorine that cannot be removed from the tank by pumping. First, the pump and its inlet must ride some distance above the bottom of the tank. Second, suction head requirements prevent pumping down to the pump inlet level. When emptying a tank, operators must first rely on removing the last of the liquid through a dip pipe. This might be under the influence of the liquid s vapor pressure or with the aid of a dry gas pad. Complete removal of chlorine to allow maintenance or tank entry always requires evacuation or gas displacement to remove the vapor and the last traces of liquid. 

A pump and cooling station was assumed to be constructed wherever the pressure was calculated to drop to a specified minimum (3.72 MPa). The horsepower was calculated to raise the pressure back to the design maximum (5.45 MPa) and to cool the fluid to the minimum specified (185 K) in preparation for entry to the next segment. Fuel gas required for pumping and cooling the fluid was assumed to be withdrawn from the suction side of the station and amounted to just under 7% of the flow. A complete description of this computer programme is given in Ref. 1. 

The NPSHr of reciprocating pumps is usually calculated for incipient cavitation conditions from the maximum entry pressure losses [18, 19], which are largely dictated by the characteristics of the suction check valve. The manufacturer s NPSHr data are in general based on these fluid mechanical effects. Typical values for the NPSHr range between 1 and 3 m for liquid CO2 (this corresponds to a pressure requirement of between 0.1 and 0.3 bar). 

Figure 9.18 Cavitation due to entry pressure losses and increasing fluid temperature (and hence vapor pressure) as fluid passes through the pump chamber. Pa, pv working chamber pressure and fluid vapour pressure pas, working chamber pressure at suction Ape, entry pressure loss I-III,...

FIGURE 3.23 Relationship between water (moisture) content (0) and pore water pressure (ij/) in a certain unsaturated soil. Pore water suction is the negative of pore water pressure, and is thus a positive quantity in unsaturated porous media. As in the case of the K-6 relationship (Fig. 3.21), the ij/-9 relationship is influenced by whether the soil was most recently wetted or dried. As porewater pressure is decreased, desaturation begins at a pressure called the air entry value, indicated by the dashed line. 

The net suction lift possible with a pump amounts to the barometric pressure less the following items (1) true vapor pressure of liquid at the pumping temperature, (2) pressure caused by weight and spring of suction valve, and (3) entry friction losses. Should this computation come out to be negative it means that a net positive suction head is necessary, that the pump can produce no lift. Centrifugal pumps should always be provided with a flooded suction (positive head), because there is no convenient way to prime or fill them with liquid and they cannot operate without liquid in the case. 

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