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Figure 2. Pumping chamber of a dairy homogenizer.

Figure 1. Modern dairy homogenizer.

Figure 2. Pumping chamber of a dairy homogenizer.

ers, they would be offset by 120 degrees. This means that the flow profile is represented by the summation of three overlapping sine curves producing some peaks and valleys, but, in general, a continuous flow will be produced. Some homogenizers have five, six, or seven plungers depending on the model.

In addition to the reciprocating plungers, the pumping chamber has suction and discharge valves. On the rearward motion of the plunger, the suction valve opens and liquid is drawn in while the discharge valve closes. On the forward discharge stroke the suction valve closes and the discharge valve opens. The plunger then displaces or pushes the liquid out of the chamber and through the discharge valve. These pump valves can be simply a ball sitting on a seat or a guided valve with a pilot aligning the valve to the seat. The piloted valve is called a poppet valve and the other a ball valve. The liquid end of the pump, especially components in contact with the liquid, is usually made of ceramics, stainless steel, or special alloys. These materials include 17-4, 15-5, 304, and 316.

Homogenizers can cover a wide range of flow rates and pressures. The range of flow rates for different machine sizes can go from 7.6 L (2 gal) per hour for a laboratory machine up to 52,996 L (14,000 gal) per hour for a large production machine. The maximum operating pressure can be 6.90 MPa (1,000 psi) up to 150 MPa (21,756 psi), but the higher the pressure rating, the lower the capacity for a given size machine. This is due to the limitation of force allowed on the drive end of the machine. For a given size machine, increasing capacity usually requires larger diameter plungers or pistons with a corresponding decrease in operating pressure due to the limiting thrust loading. Because the operating pressure is exerting force against the face of the plunger or piston, the larger diameter means that the power stroke requires greater force. Therefore, the size of the plunger or piston is limited by the maximum tolerable force on the drive end. Of course, as the pressure and capacity increase, the motor power needed also increases because the required motor power is directly proportional to the flow rate times the operating pressure.

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