pressure gauge placement?

[Ryan Mahar]

Silly question but why am I seeing pressure gauges for mainlines placed on the tree side of shut off valves? Seems to me to isolate or check the pressure of one mainline that comes off a wet/dry line, the gauge should be on the wet/dry side of the shut off. So when you close the valve on the mainline you should be seeing your 27 inches on the wet/dry and then when open the mainline valve that gauge should stay at 27 inches, if it drops then you know that line has a leak. With the opposite scenario, you have to have the valve open all the time for the pressure gauge to read anything???? Whether you have leak in that mainline, or if it is in the wet/dry or another mainline, you would not know where it is??? Right???? What am I missing???

[mellondome]

It is on the tree side so you can see if the lateral is holding vac. If you have a big vac with a little leak, you wont see it with the guage on the mainline side of the shutoff.

Multiple laterals with leaks on a marginal vac would take forever to find as the guage would never change until you were down to only one leaking lateral.

If you are walking your main to turn valves to check for leaks, you will find any leaks on the main as you will be walking past them.

[BreezyHill]

Ryan, Your thought process is good for major leaks but it is the minor likes that add up to become major leaks. Most major leaks can be found while passing by but I had one last season that many had walked by as it made no sound at all. This line had no vac gauge or valve for isolation checking. It will for 2016 season.

Remember that the lateral line will have sap and tree gases coming into the line dropping the vac...so when the valve is opened the gauge on the mainline will drop. Since this is also true when check for a leak you will need to realize it is a drop in vac relative to the drop when the system was flowing at a similar speed and was leak free.

Line of 100 taps will drop slower than a 150 tap line. So there is a learning curve to this method; but it does work well. Especially when looking for a leak that isn't revealing by walk through checks.