Question

1. screw pump test rig in detail

2. general use screw pump

3. identify its accuracy, precision and time respond in getting a reading.

4. the advantage and disadvantage of screw pump.

Answer 1

The main parts of a screw pump test rig is shown below.

Performance Test on Screw pump

Aim: To conduct the performance test and to plot the operating characteristics of screw pump
pump.

Apparatus: screw pump test­rig, stopwatch, and tachometer.

Theory:
A screw pump, also known as a water screw, is a positive-displacement (PD) pump that use one or several screws to move fluids or solids along the screw(s) axis.There are many uses for screw pumps in a variety of different industries, including Manufacturing, Mining, and Oil & Gas. Most of these applications deal with high viscosity fluid, such as oil or asphalt, or multi-phase fluid, which means there is liquid and vapor mixed together in the fluid stream.

Experimental procedure:
1. Prime the pump with water if required.
2. Open the delivery gate valve completely.
3. Start the gate valve and adjust the gate valve to required pressure and delivery.
4. Note the following readings
(a) The pressure gauge reading P kg/sq.cm
(b) The vacuum gauge reading V kg/sq.cm
(c) Time taken for every set of reading note the time taken for 3 rev. Energy meter.
(d) Close the drain valve and note down the time taken for 10cm rise of water in collecting tank.
5. Take 3 or 4 sets of reading by a varying the head for minimum to a maximum of about 3 kg/sq.cm.

Data Collection

Calculation of flow rate

GRAPH:
1. Actual discharge Vs Total head
2. Actual discharge Vs Efficiency
3. Actual discharge Vs Input power
4. Actual discharge Vs Output power

Applications for Screw Pumps

Below are some examples of where screw pumps are used:

Hydraulic and Lubrication Systems - Many lubrication systems and hydraulic systems use a screw pump. These are usually small, triple screw pumps. Lubrication and hydraulic systems like this are used for supplying lube oil to large machinery, supplying hydraulic power to high-pressure hydraulic systems or operating elevators in buildings.

Heavy Oil Pipeline - When pumping high viscosity crude oil, screw pumps can offer an ideal solution for moving it through pipelines. Able to pump higher viscosities than a centrifugal pump, and able to pump higher flows than a reciprocating pump, screw pumps are often used in these applications. In these scenarios, very large pumps are sometimes used to get to the flow rate required. These pumps are usually driven by large electric motors or diesel engines.

Multi-phase Pumping - Multi-phase pumping refers to pumping a mixture of fluid and vapor together, and is known to be one of the most challenging pumping applications. Serious damage can occur to compressors when liquid enters, just like serious damage can occur to most pumps when air enters. When built correctly, a screw pump can be a hybrid between a pump and a screw compressor, being able to handle both liquid and gas.
In order to prevent damage to a screw pump when air enters, the screws must not contact each other. For this reason, a four screw pump is usually used. In addition to this, the pump must be accompanied by a liquid boot, which is sometimes built into the pump but can easily be added externally as well. A liquid boot is a pressure vessel that collects fluid on the discharge of the pump. When an air slug comes through the supply pipe, a small pump moves the liquid from the boot and injects it into the pump. This provides slight lubrication to the screws and liner, as well as seals the clearances between the parts so the air/gas that is being pumped does not slip backward in the pump to lower pressure zones. Depending on the capacity of the liquid boot vessel, a multi-phase pump can pump 100% vapor for several minutes. Multi-phase pumping is a challenge in several different industries. Gas Well Deliquification and Propane Cavern Storage are common challenges in the Oil & Gas industry.

Advantages of screw pump:
1. Wide range of flows and pressures
2. Wide range of liquids and viscosities
3. Built-in variable capacity
4. High speed capability for freedom of driver selection
5. Low internal velocities
6. Self-priming with good suction characteristics
7. High tolerance for entrained air and other gases
8. Minimum churning or foaming
9. Low mechanical vibration, pulsation-free flow, and quiet operation
10. Rugged, compact design - easy to install and maintain
11. High tolerance to contamination in comparison with other rotary pumps

Disadvantages of screw pump:
1. Relatively high cost because of close tolerances and running clearances
2. Performance characteristics sensitive to viscosity change
3. High pressure capability requires long pumping elements