When threading metal threads into a metal coupling, pipe sealant or Teflon® tape is recommended. Due to potential compatibility problems, when sealing plastic threaded units, a compatible pipe sealant such as No More Leaks™ from Permatex® is recommended.
When threading a plastic level switch into a metal coupling, the installer should use a suitable wrench and tighten the threads 1 to 1-1/2 additional turns past right hand tight. Over torquing of the threads will result in damage to the plastic mounting plug.
The Effect of Thread Engagement on Actuation Points
The length of mounting threads engaged at installation is important in calculating switch actuation points and the actual length of stem extending into the tank. Use the chart below to find the thread engagement length (T) for a given NPT size. Factor the T dimension into any calculation of switch actuation levels (L) and overall length (L°).
Definition of Variables Used in Examples Below
A = Mounting length.
T = Thread engagement.
P = Distance from coupling (bung) top to inside surface of tank or bracket.
L = Switch actuation level as measured from inside surface of tank or bracket to fluid surface.
L1 = Switch actuation level, nominal, as measured from bottom of mounting (based on a liquid specific gravity of 1.0).