- Closed-toed shoes are required in the Hydrotechnical Lab
- Safety glasses are required in the Hydrotechnical Lab
- Incorrect use of the apparatus may cause water hammer which has the potential to burst the pipes
Link to Lab 2 Manual CIVL315_Lab 2_ Manual_Sep2018_Final
The apparatus is a recirculating system with various fittings. Figure 2.1 shows a schematic of the system. The pump circulates water from the sump, which has two chambers. A V-notch weir separates the two chambers and can be used to measure the flow rate. There are pressure taps at a number of points around the circuit. Most are simple water manometers, however there are 3 special manometers at the end of the apparatus used to measure differential pressures. The red liquid is water coloured with dye. There are also two digital pressure gauges installed in the system, which measure the pressure before and after the pump.
Figure 2.2 Pump curve provided by the manufacturer. You need to determine the impeller diameter for the pump in the lab in order to use this.
Setting up the equipment
Check that there is sufficient water in the reservoir. The water level upstream from the V weir should be just touching the bottom of the “V”. The water level in the reservoir after the weir should be about six inches below the upstream reservoir.
If there is insufficient water in the reservoir (so air is being sucked into the lower pipe) add some with the green hose attached to the wall.
Caution: Unlike other experiments, which only have a valve on the outlet side of the pump, this apparatus also has one on the inlet side. To avoid damaging the pump, ensure that the inlet valve A is fully open and that the outlet valve B is fully closed before starting the pump. If in doubt, ask your TA.
Part 1 – Losses Around the Circuit
Before you turn on the pump, record the “zero” water level in the sump, which is where water sits at the very bottom of the V-notch. You will measure h (depth of water above the V-notch) relative to this level.
Switch on the pump and slowly open the outlet valve B until Manometer 1 approaches a full scale reading (approximately 2 inches from the top). Ensure that there are no bubbles in any of the tubes leading to manometers before taking any readings. Record all manometer readings around the entire circuit and also measure the flow.
Take some time to study each of the different types of manometers and to observe where each is connected in the system. Wherever necessary, measure the difference in height between the measuring point and the manometer. It will be necessary to correct all readings so that they are in the same units above or below a common datum. Make sure that you specify a datum and take all the necessary measurements.
The two digital pressure gauges display the negative pressures in inches of Mercury and the positive pressures in psi units. Do not forget to convert all your readings to the same system of units. Note: All measurements in this lab are to be reported in Imperial Units.
The inlet (A) and outlet (B) valves are non-standard gate valves. Observe the configuration and discuss with the TA.
Part 2 – Pump and System Performance
Create a pump curve (e.g. Figure 2.2) for the pump by making appropriate measurements over the full range allowed by the apparatus. Pay close attention to the instructions provided in Part 1 above to determine the full range. It’s up to you to determine how many increments within the full range are needed to adequately characterize the pump performance.
Part 3 – Cavitation and Air Entrainment
Note: This section requires the assistance of the TA. Please consult with them before proceeding in this part.
- Adjust Valve B so the Manometer 1 reaches full height (approx. 136 inches).
- Slowly close Valve A until cavitation.
- Observe the changes in pump and system performance during cavitation.
- Observe the mechanical effects of cavitation.
- With Valve A completely open, use the baffle plate to entrain a vortex. Observe the effects on pump performance.
Part 4 – Shutdown Procedure
- Be sure Inlet Valve (A) is open fully.
- Close Outlet Valve (B) completely.
- Turn off the pump.
- Turn off the pressure gauges.
JF Atwater, V Martin ©2010 UBC Department of Civil Engineering