2 non positive displacement pumps non positive

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Chapter 5 / Exercise 19
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2. Non-positive displacement pumps: Non-positive displacement pumps differ significantly from positive displacement pumps in that the flow rate varies greatly with changes in the flow resistance. Flow rate can vary from zero to maximum flow without affecting the operation of the pump. There are large clearances between the moving and the non-moving parts of the pump, therefore the fluid can slip back into the clearance spaces. Pumps of this type are unable to achieve the elevated pressures that positive displacement types can. Pump efficiency: The efficiency of a pump is an indication of the pump’s performance under certain operating conditions. The overall pump efficiency is a product of the volumetric efficiency and the mechanical efficiency. Volumetric Efficiency = Actual volume flow rate Theoretical volume flow rate = Q Q A T x 100 (1) Volumetric efficiency is a function of internal slippage or leakage. In general, non-positive displacement pumps have less volumetric efficiency than positive displacement pumps.
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Chapter 5 / Exercise 19
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MMET - 303 Mechanical Efficiency = Theoretical power out Actual power in = P Q N T T . . x 100 (2) where, P is in Pa Q T is in m 3 /s T is in N-m N is in rps Mechanical efficiency varies with the amount of internal friction in the pump. Overall efficiency then is the product of the two and can be expressed as; Overall Efficiency = Volumetric Efficiency x Mechanical Efficiency = ¸ ¸ ¹ · ¨ ¨ © § Power Input Pump Actual Power Output Pump Actual (3) The actual power out is given by; Actual Power out = P x Q A (4) The actual power input to the pump & motor combination is given by the electrical power input to the pump; Actual Power in = Electrical Power input (Watts) Figure 1: External Gear Pump
MMET - 303 Figure 2: Experimental Setup Legend: Procedure and Task: Part A: External Gear Pump: Design and Construction 1. Review the construction of the external gear pump. 2. Describe the operation. Part B: Internal Gear Pump: Design and Construction 1. Review the construction of the internal gear pump. 2. Describe the operation
MMET - 303 Part C: Pump Efficiency of a Vane Pump 1. Make sure trainer is off. 2. Connect the wattmeter; make sure it is also off. Instead of a wattmeter, a fluke meter can also be used. 3. Set up the hydraulic circuit that will take the flow from the pressure manifold through the flow restriction valve to the flow meter and back to the tank. Also, set up a line from the manifold to the pressure gage. 4. Turn on wattmeter. 5. Turn on pump. 6. Open completely the flow restriction (needle) valve. 7. Record the following: a. Outlet Pressure, kPa b. Flow Rate (Q), l/min c. Electrical Power, Watts 8. Slowly close the flow restriction valve to increment the pressure 100 kPa , repeat step 7 9. Repeat Step 8 until the reading in wattmeter is about 950 Watts Part D: Pump Curve for a PD (AODD: Air Operated Double Diaphragm) Pump 1) Turn the valve on the suction side completely open. Keep the discharge valve closed.

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