Guide pipe / stilling well for top mounted displacer level switch


Thread Starter

anand s

dear all

please let me know how to choose the length of stilling pipe / guide pipe for a top mounted displacer type level switch for sump. Is there any thumb rule? or any Standard practice to select the length of the guide pipe? Is there any practice that the guide pipe will be grouted at the bottom of the RCC sump? Is so what should be the depth of the tank? Also please tell the mounting arrangement at the top of the sump if it is of flanged type. Please note that the sump is at atmospheric pressure. How about the factor called Hydrostatic pressure? does it affect the level if the guide pipe is grouted? If so, what is the compensation formula for that?

please reply

hello -

Displacer Type. You're talking about a top mounted snap action type switch with one or more floats hanging on a wire or rod. Liquid rises – floats get light – switch snaps.

The tube is only needed if the liquid sloshes in my opinion. Nothing can stick as the floats are on a wire or rod. The tube can be anything that allows the floats to move inside. The scum build up inside the tube it may stop the float action. In water use PVC with a flange glued to the top. Use the flange as a base for the snap switch box. It is probably only a NEMA 4 box with 4 boltholes.

The tube can be open but you may want some vent holes so the liquid inside the tube stays equal with the outside.

We build slosh / support tubes for our magnetic flag level switches and multi level controls and your only concern would be mounting it to the vessel and making sure the floats don’t stick.

We build a sump switch for dirty applications with the float and rod below a base with adjustable switch points above. I think a picture is in our cat at
2 nd. page near the top - 2000 Cat pdf file.

So – the only thing to be concerned about is floats touching the side, how to mount and venting. If I read your question correctly..
Bob Hogg
Dear Mr. Bob Hogg

Thanks a lot for ur immediate prompt reply. Yes u are right. This ia a top mounted snap action type switch with one or more displacers hanging on a wire.

But my concern is not that float will stick.

My concern is about the length of the guide pipe. My application is in a Raw water /Fire water sump level and some more sump level which contains only clear water and it is not for dirty /sewege applications,where I am going to mount these level switches.

The depth is about 8 meters. I am going to CS guide pipe of 4inch size pipe.

My apprehension is that whether it requires any grouting at the bottom of the tank and top mounting i am planned to go for flanged.

Should the guide pipe length cover the entire depth of the sump(since here the depth is more) or enough it only covers the minimum level of the sump.

Once again thanks for ur reply


anand s
hello -
I guess you would want the entire length - as the float would flop around. Ground the bottom? I would say no as you need the thing to drain - if I understand correctly.

It is only acting as a slosh tube - right??

Thanks Bob Hogg