A pipe laser is one of the simplest instruments on a groundworks site, and one of the easiest to set up wrong. Almost every call we get about a pipe laser reading badly comes down to something in the set-up rather than the instrument. Here is the routine we teach on the hire desk.
Before you go down
- Check the batteries and the target. A flat battery halfway through a run means a resection. Charge the pack overnight and take the spare. Make sure you have the right target for the pipe diameter, and that it is clean.
- Know the numbers. Have the invert levels at each manhole and the design gradient written down, not on a phone that has just gone flat. Convert the gradient to a percentage if the laser wants one: 1 in 100 is 1 per cent, 1 in 40 is 2.5 per cent.
- Confirm the direction of fall. On most lasers a positive grade means the beam rises away from the instrument. If you are setting up in the downstream manhole and shooting uphill, that is what you want. Setting up in the upstream chamber and shooting downhill needs a negative value. Getting this wrong is the single most common fault we see.
In the chamber
- Get the base solid. Use the trivet or the manhole pole, not a lump of brick. The laser must sit on the pipe invert or on a known offset above it. Note the offset if there is one.
- Set the line. Sight the laser up the run from behind using the line-of-sight adjustment, or use the automatic alignment if the model has it. Put the target in the first pipe and confirm the beam is centred before you touch the grade.
- Enter the grade. Type the percentage in and check the display shows the sign you expect. Let the laser self-level. Do not move it while it settles.
- Check at a known point. Place the target on the invert at the far end of the first pipe length and confirm the beam hits the centre. If you have a staff and a level, take a reading on the beam at 10 m and compare it with the design invert plus the rise you expect over that distance. This takes two minutes and catches almost everything.
As the run goes in
- Recheck the target every few pipes. Heat shimmer in a long run can bend the beam a surprising amount, especially over water in the invert.
- If anyone kicks the tripod or the trivet, start again. Do not try to nudge it back.
- When the run is finished, note the final reading against the design level before you strip the laser out. It is your evidence if there is a query later.
Common faults we see on hire returns
Beam wanders: usually a loose base or a flat battery. Cannot hit the target at range: usually condensation on the lens or a green-beam laser used in bright daylight without the right target. Grade reads wrong: almost always the sign, occasionally a laser that has been dropped and needs a calibration check.
If a pipe laser has been dropped, do not use it until it has been checked. We can turn a calibration round in a couple of days and put a hire unit in the van in the meantime. Ring 01522 697777.
