Hydraulic bench is a volumetric flow measurement apparatus that consists of a water receptacle present at the bottom, through which water is pumped up to an open channel through a control valve by a centrifugal pump. This water is finally discharged into the volumetric tank and the change in level of water in the volumetric tank, as given by the calibrated scale, gives the flow rate.
A hydraulic bench may also be used to supply water to other apparatuses for their working.
General Working of Hydraulic Bench
The figure shows the general working of a hydraulic bench. The water is stored in a sump tank. When the motor is turned on, this water is pumped up to the open channel through a suction pipe which is kept transparent to identify the onset of cavitation process, in case it commences.
This open channel is the water source for the volumetric tank and therefore, the water flows from the channel to the tank present at a relatively lower elevation. Finally, this water is made to outflow the tank back into the reservoir or sump tank.
Prior to discussing in detail, the different parts of the apparatus, there are a few technical details that are provided by the manufacturer. These include the following,
- Pump Type
- Maximum Head
- Maximum Flow
- Motor Rating (kW)
- Sump Tank Capacity (Liters)
- High Flow Volumetric Tank (Liters)
- Low Flow Volumetric Tank (Liters)
- Height of working surface above floor level
Parts of Hydraulic Bench Apparatus
The following labelled figures show different parts of a hydraulic bench.
- On/Off Switch for Motor
- Discharge Control Valve
- Sight Tube and Scale
- Volumetric Tank
- Open Channel
- Centrifugal Pump
- Sump Tank
- Open Channel
- Flow Control Valve
- Inlet Stilling Baffle
- Tank Stilling baffle
- Dump Valve Handle
1)On/Off Switch for Motor:
In order to start the motor of centrifugal pump, the motor switch is turned on. This results in initiation of the pumping process.
2)Discharge Control Valve:
This valve controls the flow rate into the volumetric tank. A clockwise rotation tends to decrease the discharge and a counter clockwise rotation increases the flow rate.
3)Sight Tube and Scale:
A sight tube present close to the discharge control valve gives an instantaneous value of flow rate in to volumetric tank and the value can be read from the scale present beside the tube.
This tank is present downstream of the open channel. It receives water from the open channel. However, the flow rate into this tank is governed by the discharge control valve. The change in level of water in the tank is determined by noting the difference in level of water given by the sight tube.
This channel receives pumped water from the sump tank and the flow rate into this channel is governed by flow control valve present beneath it.
This pump converts the mechanical energy of motor into hydraulic energy by the action of centrifugal force. As a consequence, the water is pumped up from the sump tank and is permitted into the open channel by the flow valve.
A sump tank is actually a water reservoir present at the bottom of the hydraulic bench. The water is pumped from the sump tank into the open channel. In addition, when the water level in the volumetric tank reaches a certain value, it empties into sumo tank and the process is repeated.
8)Flow Control Valve:
This valve controls the flow from the sump tank into the open channel.
9)Inlet Stilling Baffle:
It acts as a stopper for water to retain in the open channel. When water travels up into the open channel, the inlet stilling basin helps dispersing the water stream, thereby, keeping water in the channel.
10) Tank Stilling Baffle:
When water enters the volumetric tank from the open channel, a tank stilling basin ensures smooth gliding of water. If this is not provided, the water that strikes the tank bottom may produce some local turbulence. This may result in continuous fluctuation of water level that can be seen from the sight tube. Therefore, the discharge measurement may give misleading results.
11) Dump Valve Handle:
A dump valve handle is used to drain water from the volumetric tank back into the sump tank. This can be achieved by raising the handle. Additionally, the overflow in the volumetric tank puts a limit on its maximum capacity, after which water dumping indispensable.
Discharge Measurement in Volumetric Tank
In order to measure the discharge into the volumetric tank, measure the initial level of water on the sight tube. Once the water is discharged in the tank from the open channel, note the final reading on the scale. Also measure the time taken for water to fill the tank to a certain depth.
The discharge can then be mathematically calculated as,
Uses of Hydraulic Bench
Hydraulic bench can be employed for a number of hydraulic operations that include the following:
- It ensures the provision of uninterrupted and controlled supply of water for various laboratory experiments
- It helps measure the flow rate or discharge.
- It recirculates water and therefore, behaves as a self-contained and portable mobile unit.
Applications of Hydraulic Bench
Hydraulic bench aids in determining different properties of fluid and fluid flow, for instance;
- For determining the Coefficient of Velocity,
- For determining the Coefficient of Discharge,
- For determining the Coefficient of Contraction,
- For studying flow characteristics over weirs and notches
- For finding the metacentric height
- For finding head losses through pipes
- For verification of Bernoulli’s theorem
Precautions when Handling Hydraulic Bench
- The operating instructions must carefully be read and understood preceding the usage.
- It is preferable to handle hydraulic fluid wearing gloves and safety googles.