WorldWide Drilling Resource

78 SEPTEMBER 2014 WorldWide Drilling Resource ® simply use a compressed air source with the end of the tube near the bottom of the tank, then “tee” the pressure sensor somewhere in this line. It’s great, but there’s one caveat: It’s not very accurate. But it doesn’t need to be, either. In most tank fill applications, all the customer is concerned about is that water is maintained in the tank by turning the fill pump on and off without overflowing. It’s not very accurate be- cause most pressure transducers (sen- sors) are a 1% tolerance. For a 0-100 psi full-scale pressure sensor, it’s +/- 1 pound accuracy. When dealing with the water column, it’s +/- 2.309 vertical feet of water. When the pump is off and the water isn’t moving, we can get a pretty accurate reading. Just divide the psi by 0.433 and you will get the exact vertical col- umn of water, and you can adjust your “on” settings accordingly. Turning the pump off is a little tougher because the pressure in the pipe going to the bottom of the storage tank will rise, but how much it will rise cannot be predicted. However, it is consistent and repeatable and, as the water level in the tank rises, so will the pressure in the fill pipe. Simply adjust the “off” setting at the pressure point you want the pump to turn off. This is easy to do with the electron- ics we have today because delays are required to prevent rapid on-off cycling. The delays slow the reaction time of the pump and provide stability. If you want to maintain the tank level at +/- 1 inch, there are several other methods out there to do it - from floats, probes, ultrasound, and conductive tape in the tank. They all work, but are 10 times the cost - not to mention the extra installa- tion time, expense, and reduced reliability because they are more complicated. Just about everything in life has to do with choosing good compromises, given the task at hand, and product development is no exception. Sure, some- thing may not be perfect, but given the task at hand, it will do the job for a rea- sonable price. And that’s the objective. Britt Britt Storkson may be contacted via e-mail at admin@ worldwidedrillingresource.com Storkson cont’d from page 72.