Pumped liquid

Diffusion pumps operate at veiy low pressures. The ultimate vacuum attainable depends somewhat upon the vapor pressure of the pump liquid at the temperature of the condensing surfaces. By providing a cold trap between the diffusion pump and the region being evacuated, pressures as low as 10 mmHg absolute are achieved in... 

The above graphie shows three identieal pumps, eaeh designed to develop 92.4 feet of head. When they pump liquids of different speeifie gravities, the heads remain the same, but the pressures vary in proportion to the speeifie gravity. 

This type of pump is similar to others exeept that the impellers diseharge into a diffuser hell ty pe housing instead of the volute. The diffuser has multiple veins or ribs that direct the pumped liquid through a eolumn or into the next impeller (Figure 6-10). 

These pumps normally use sleeve bearings lubricated with oil, grease, or even the pumped liquid (except for abrasives). 

These pumps incorporate an electric motor whose rotary assembly is hermetically sealed inside a stainless steel or exotic alloy can. The motor, pump shaft and bearings all operate wet inside the pumped liquid as show ii in Figure 6-12. 

The pump impeller receives the pumped liquid and imparts velocity to it with help from the electric motor, or driver. The impeller itself looks like a modified boat or airplane propeller. Actually, boat propellers are axial flow impellers. Airplane propellers are axial flow impellers also, except that they are adapted to handle air. 

This type of seal mounts onto the shaft or sleeve inside the seal chamber and pump. The pumped liquid comes into eontaet with all parts of the seal and apiproaehes the outside diameter of the internally mounted faces keeping them lubricated. The environment outside the pump approaches the ID of the seal faces. 

This type of seal has the rotary component and face mounted outside the seal chamber. The springs and drive elements are outside the pumped liquid. This reduces the problems associated with corrosion and the accumulation of pumped product clogging the springs. This seal is popular in the food processing industry. The pumped liquid arrives to the inside diameter of the faces and seals toward the outside diameter. The environment outside the pump approaches the OD of the face union. Pressures are limited to about 35 psig. Sometimes this. seal can be mounted either inside or outside the pump. This seal is easy to install, adjust, and maintain. It permits easy access and cleaning of the pump internal parts, often required in the food processing industry. 

Double seals require some type of support system. The reason is simple. With two seals mounted onto the same shaft, one seal is the principal or primary seal and the other becomes the secondary or back up seal already installed. If the primary seal is performing its function and sealing the pumped liquid, the. secondary. seal would be running dry, overheat, burn and self-destruct. Then when the crucial moment comes, we won t have a second seal to assume the ftinctions, which was the original reason to consider a dual seal. 

For most applications, the balanced, o-ring cartridge seal will adequately handle every pump, liquid, and condition in a modern industrial process plant. There are, however, some industrial pumping applications that will present problems to even the best of mechanical seals. Should one of these applications cause the seal to give less than desirable performance, the next step to take in extending the service life of the seal (and ultimately the pump) is to install some type of environmental control to protect and isolate the seal components from the fluid. Let s consider some difficult sealing applications. 

Separating the seal environment from the pumped liquid... 

This method requires a source of water or steam for the quench. The pumped liquid may contaminate the drainage. If so, it should be discarded. 

Inadequate Pressure. Not enough velocity. Air or gases in pumped liquid. Impeller diameter too small Worn or damaged impeller Incorrect rotation... 

Lubricity. In any mechanical seal design there is rubbing motion between the dynamic seal faces. This rubbing motion is most often lubricated by the fluid being pumped. Therefore, the lubricity of the pumped liquid at the given operating temperature must be considered to determine if the chosen seal design and face combination will perform satisfactorily. 

A current vehicle fuel system designed for evaporative emission control should address enhanced SHED, running loss, and ORVR emission level requirements (see Table 1). A typical vehicle fuel system is shown in Fig. 4. The primary functions of the system are to store the liquid and vapor phases of the fuel with acceptable loss levels, and to pump liquid fuel to the engine for vehicle operation. The operation of the various components in the fuel system, and how they work to minimize evaporative losses during both driving and refueling events, is described below. 

Helieal serews operate in tlie laminar range at normally high impeller to vessel diameter ratio (D /D ) with a radial elearanee equal to 0.0375 D. The impeller usually oeeupies one-third to one-half of the vessel diameter. They funetion by pumping liquid from the bottom of a tank to the liquid surfaee. The liquid returns to the bottom of the... 

Figure 12-26. The SIMULAR reaction calorimeter. Features include pumped liquid feed, gas mass flow control, gas evolution measurement, and distillation equipment. (Source Hazard Evaluation Laboratory Ltd.)...

On the fifth day, the emergency team began to pump liquid nitrogen into the space under the reactor, in part to cool the debris, but also to put out the fire with its inert atmosphere. 

Figure 3-59 shows the typical cross-section of this type of pump. In this pump liquid is pumped by the action of the rotation of the two eccentrically located piston surfaces. There is no contact between the piston surfaces. 

Run-around coils. Where the incoming and outgoing air streams are remote it is necessary to use a run-around coil to couple them. A pumped liquid to a heat exchanger in the cold stream connects a heat exchange coil in the warm exhaust. The effectiveness can be up to 60 per cent. 

In most applications, it is relatively straightforward to confirm the total elevation change of the pumped liquid. Measure all vertical rises and drops in the discharge piping, then calculate the total difference between the pump s centerline and the final delivery point. 

Determining the total friction loss, however, is not as simple. Friction loss is caused by a number of factors and all depend on the flow velocity generated by the pump. The major sources of friction loss include friction between the pumped liquid and the sidewalls of the pipe valves, elbows, and other mechanical flow restrictions or other flow restrictions, such as back-pressure created by the weight of liquid in the delivery storage tank or resistance within the system component that uses the pumped liquid. 

In some cases, friction losses are difficult to quantify. If the pumped liquid is delivered to an intermediate storage tank, the configuration of the tank s inlet determines if it adds to the system pressure. If the inlet is on or near the top, the tank will add no back pressure. However, if the inlet is below the normal liquid level, the total height of liquid above the inlet must be added to the total system head. 

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