Spirit levels are used for checking and leveling the surfaces during installation and checking.
Figure 1: Spirit Level.
A spirit level is a tool used to measure and verify the alignment of a surface, ensuring it is either perfectly horizontal (level) or vertical (plumb). It works on the principle of gravity and uses a sealed vial filled with liquid and an air bubble. The bubble moves within the vial and aligns with the center markings when the surface is correctly positioned.
Construction of Spirit Level
A glass tube, whose surfaces are grounded, is fixed in a frame as shown in Fig. 1. A glass tube has got radius ‘R’ which is very large and filled with ether liquid, as well as ether bubble (vapor). Its construction includes:
- Body: Typically made of wood, metal, or plastic, providing durability and a straight edge.
- Glass Tube (Vial): A sealed, curved, and transparent tube filled with liquid (alcohol or oil) and a bubble of air.
- Ether Vapor Bubble: The bubble in the vial indicates the level when it is centered between the marked lines.
- Cross Spirit Level (90°): A secondary vial positioned at 90° to check for vertical alignment.
- Markings: Lines on the vial help determine precise leveling.
Working Principle of Spirit Level
The spirit level operates based on gravity:
- The glass vial is slightly curved, and the bubble naturally moves to the highest point.
- When the surface is level or plumb, the bubble aligns perfectly between the marked lines on the vial.
Working of Spirit Level
Figure 2: Spirit Level.
The position of the bubble in the tube will be always at the topmost level which is the principle of working of the spirit level. Fig. 2 shows the principle sketch of spirit level. In this, R-radius of curved glass tube A – is the topmost position of the bubble at horizontal position of spirit level. If bubble moves one division, i.e. from B to B’, the angle of tilt is θ. The level sensitivity per division i.e. the tilt causing the displacement of bubble by one division of the scale is expressed in mm per meter, e.g. 0.02 mm/meter.
For measuring very small angle in terms of seconds, the movement of bubble in terms of divisions is measured and multiplied by least count/level sensitivity. If R is the radius of curvature of the inside surface of the glass tube and α is angle of tilt in radians,
Displacement of bubble, l = R · α
The sensitivity of a sprit level depends on R As R increases, sensitivity increases. If α is expressed in seconds,
\[l=\frac{R{\alpha }”}{206265}\]
[1 radians = 206265 seconds of arc]
If the space between two lines is 2 mm and for a radius of R = 206 m,
\[{\alpha }”=\frac{2\times 206265}{206\times 1000}={2}”\]
This indicates inclination of 2″ of a spirit level will cause a bubble to move by 1 division or 2 mm. Spirit levels are to be handled very carefully and they are sensitive to temperature.
Advantages of Spirit Level
- Easy to use and provides quick results.
- Lightweight and portable.
- Requires no power or complex setup.
- Durable and reliable for long-term use.
- High accuracy for both professional and DIY applications.
Uses of Spirit Level
- Checking the horizontal and vertical alignment of surfaces.
- Ensuring the proper leveling of furniture, tiles, and construction work.
- Plumbing and carpentry for installing shelves, cabinets, and frames.
- Aligning machinery and industrial equipment.
- Calibration tasks in surveying and engineering.
Care of Spirit Level
The following care is to be taken when spirit level is used.
- Spirit level should be used properly for avoiding errors.
- Temperature variation may effect on the accuracy of spirit level.
- Calibration should be carried out time to time.
- Care to be taken to avoid deformation of glass tube to avoid error.
- It should not made vertical during handling.
- As it contains glass tube, should be handled carefully.
Types of Spirit Levels
- Standard Spirit Level: Used for general leveling tasks.
- Torpedo Level: A compact version for tight spaces.
- I-Beam Level: A durable and lightweight option, often used in construction.
- Box-Beam Level: Known for high accuracy, suitable for professionals.
- Cross-Check Level: Features vials for both horizontal and vertical leveling simultaneously.
- Digital Spirit Level: Includes a digital display for precise angle readings.