Tank pressure control is one application we are frequently asked about. A few months ago I introduced my list of the top 5 common causes of pressure control issues on tanks, and I have been providing some solutions for each problem.
To recap, the top 5 common causes of pressure control on tanks—in no particular order—are: (Click the links below to review the solution)
1) Variable or incorrect regulator inlet pressure
2) Stored product causing plugging
3) Overlapping or “tight” setpoints
4) Lack of self-draining sensing lines or low point drains
5) Lack of continual maintenance programs
#4 Lack of self-draining sensing lines or low point drains
All manufacturers of tank blanketing regulators will recommend that the regulator be located on top of the tank for optimal performance. The reason is twofold: first, to get the sensing element (the regulator) as close to the vapor space where the pressure is being controlled and, second, elevating the regulator above the tank allows for the sensing line to be “self-draining.”
Many times when conducting a tank pressure control survey we find sensing lines with low points or sloped down toward the regulator.
Low points in a sensing line can cause liquids to build up in the low point and can lead to the regulator being unable to sense the tank pressure. When the sensing line is sloped down toward the regulator—similar to the photo above—the liquid can end up in the diaphragm area, which can cause inaccuracy.
Sensing lines should be sloped downward toward the tank to prevent condensation build-up and be as short and straight as possible. This is especially critical when sensing pressures 1 inch w.c. or less.
But, what if you have no choice but to have the regulator mounted below the tank connection or maybe at grade? I previously addressed this topic in another post: 3 Things to Consider before Installing a Tank Blanketing Regulator at Grade. Number 2 was the installation of low point drains AND, more importantly, a continual maintenance schedule to drain the low points on a regular basis.
Typical low point drains involve the installation of a valve at the lowest point of the sensing line and can be opened to drain the liquid. Another method seen in the field is the installation of a liquid trap that is open to atmosphere. While both of these methods require a continual maintenance schedule to either drain the liquid or check the liquid level, the liquid trap can tend to go longer between inspections since it is open to the atmosphere.
If you have any questions about your tank application, please reply to this post, reach out to me via email, or contact your local sales representative. Stay tuned for my final post in this series where I discuss the need for continual maintenance programs on your tank pressure control systems.