The quick answer is yes!
However, there are limitations that differ between the WTC and WTCC series well caps, we will cover these differences in more detail below.
The WTC-A-xx Aluminum and WTC-C-xx Cast Iron series are not recommended for sealing to an off-spec well casing. These caps use an O-Ring to seal to the O.D. of the well casing, and have very limited capability to seal a larger annular gap as the compression is fixed due to the set tapper of the lower ring.
The better option is to use the WTCC-A-xx Aluminum and WTCC-C-xx Cast Iron series. These caps use a wide gasket to seal to the O.D. of the well casing, and they provide the capability to expand in thickness to fill the larger annular gap when compressed by tightening the bolts. For these reasons we recommend the WTCC caps for sealing to an off-spec casing having a smaller OD than the published casing size.
NOTE: The WTCC caps do have limitations as to how much smaller the O.D. can be before it fails to provide a tight seal to the well casing. Unfortunately, there has been very limited field testing, therefore there is not much information available to cover all the specific scenarios.
However, based on past experience we do know that a WTCC-A066 well cap designed for 7” OD well casing will seal on a 6.90” OD PVC well casing (7.0” -6.9 “= 0.10” / 2 = 0.050” additional gap per side will compress and make a very good seal). This is just under 1/16” compression per side (all around the circumference) more than the optimal size casing.
Therefore, based on this theory our WTCC-A05 well cap designed for 5-9/16” OD well casing is expected to seal on a 5.50” OD well casing (5.5625” – 5.50” = 0.0625” / 2 = 0.0312” additional gap per side will compress and make a very good seal). This only requires 1/32” reduction all around the circumference than the optimal size casing of 5-9/16”.
The only way to be 100% sure is to conduct a physical test. Boshart is willing to do this testing, if the customer would provide a minimum of 6” length of casing that they are planning to use the well cap on.
Conclusion:
For sealing to a well casing that is smaller than the well cap is designed for:
- Use the Boshart WTCC series (wide gasket) well caps.
- The WTCC series caps are very likely to seal on a smaller well casing as long as the well casing is not more than 1/8” smaller in O.D. (1/6” per side) than the published well casing size.
- In the worst-case scenario, the well cap fails to tighten securely or provide strong pull-off resistance - both of which are essential indicators of a proper seal. In that case, there is a back up solution that is commonly used to accommodate odd / off-spec well casings up to1/4” to 3/8” smaller in diameter.
SOLUTIONS:
Option #1 - Increase the well casing diameter to the desired casing O.D. by wrapping as many layers of 2” wide PVC pipe wrap tape (Part No. PW2-10NL) around the top 2” of the well casing to ensure the gasket can compress firmly against the tape. The tape should stand up well as it is compressed tightly between the well casing and the wide sealing ring of the WTCC series well cap. The tape is protected from the UV rays and the elements, and deterioration is not expected.
Option #2 - Add a short section of properly sized O.D. well casing. This can be joined to extend the existing casing.
Additional Resources:
https://support.boshart.com/how-do-i-install-a-wtc-series-well-cap
https://support.boshart.com/how-do-i-install-a-wtcc-series-well-cap
https://support.boshart.com/four-reasons-the-wtcc-a-or-wtcc-c-watertight-well-caps-are-the-1-choice