I have very limited knowledge on pipe lasers in general. All my experience with them is new sewer installs where everything is staked out and grades are on the blue prints. The challenge I am faced with now is I need to rehab an active sewer, the inspector really wants me to use a pipe laser but I do not know how to sit one up in an existing active sewer line. There is no grades to follow on paper other then "match existing grade" however no one knows what current grade is. I have to be dead on as we are tying into exiting manholes, any advice is greatly appreciated.
Active sewer line doesn't sound much fun to set up in, would want to set it up above the flow line to keep it high and dry, measure flow line to laser, go to next manhole and match that measure and put it on line. If the top of the pipe is exposed maybe you could set up on top of the pipe, measure difference between laser light height and top of pipe and then dial it in to match that elevation on the other end, and put it on line. Then you'd check the new pipe from the top of it to the laser.
shoot the flow line of each end of the line in the invert of the manholes that you are tying into. determine difference in elevation and divide the total distance. ie....... 20-19=1 divided by the distance, say 150 feet 1/150=0.0066" fall per foot. enter the slope on your laser and you can verify by placing your target on the proposed flow line and shoot both ends.
zhkent sounds kinda like what I was thinking. let me check to see if I got this correct, shoot both inverts with my rotary laser divide distance to get grade per foot, lay first stick of pipe set laser on top of new pipe and go from there? my problem with this is how do I get the first stick perfect? just use the rotary laser and hope for the best? if you don't mind my asking what part of ks are you in?
I would put a ball in stop flow for a time being if it's that much. Doing so if it starts to back up you may have to bypass or temporary ty back in to let run. Put the laser in the pipe like normal. Get the grade close (maybe even a tad high), set first pipe line up may need to shake down. We did a 48" rehab by laying it backwards (digging down hill) with 4 18" bypass pumps running 24-7. We would do about 1800 feet at a time. Then move everything
wrc, just south of you in Burlington.
Rise divided by run x 100 gives percent to set laser at. On live sanitary some times we could pump from tie in manhole to the one we are going to. Other times just dig sumps as we went to keep myself clean.
Be careful about going into existing manholes, it's a confined space and air quality might be dangerous.
set first pipe with 4 foot level and folding grade stick. Get laser and target set. Then with plumb Bob move laser left or right until the string on the plumb bob and lath at finish line split the laser beam.