Water Pipelines: Why Pressure Fed Systems Fail and How To Fix Them

For those of you dealing with pressure-fed systems, you’ve probably learned the hard way that water hammer is not your friend.  You’d be surprised just how heavy a mile of water is in a 1” diameter pipe.  Take a guess right now before we tell you.  In fact, it’s approximately 1800 pounds, or nearly one ton of water.  Water is nearly incompressible.  What this means is that in a closed volume, it has no give.  You can’t squeeze it into a small space like you can with air.  Even though the water doesn’t have much diameter, it still behaves like a single mass contained within that pipe.  How hard is it to get that water mass moving?  Well, if you apply hydraulic pressure with a pump on one end, only a few seconds. But if you suddenly try to stop a one ton mass, you’re going to have trouble.  This is why floats on the end of a long pressure pipeline are so tricky to set up.  If the float closes too fast, then a huge pressure buildup can occur near one end of the line, and the pipe could crack.  Imagine you have a one ton rod slamming into a brick wall.  Even if it were moving slowly (say, a couple feet per second), that rod would cause massive damage.  Water may not look hard, but when trapped inside a pipe, it is strong enough to split steel, as you may have found out in the winter months.  So let’s say you have a float which closes slowly.  Why then does the pressure switch back at the well head seem to be so wonky?  Sometimes it cycles on and off, and behaves in erratic ways.  The issue here is because of what we call pressure waves.  You do realize that sound can move through water just like it can through air.  When a float closes, a pressure wave is generated at the end of the pipeline.  That wave travels back up toward the pump, which temporarily increases and then decreases the pressure sensed by the switch.  The pipe itself will expand slightly and dampen the wave over time.  However, the wave can still bounce back and forth inside your pipeline.  These pressure waves travel at the speed of sound in water, which is about 4800 feet per second.  This means the wave could bounce back and forth inside a 1 mile pipe roughly every two seconds.  When the wave leaves, a low pressure trough forms, and it can cause the well switch to activate.  To dampen the wave, you have to have some sort of surge arrestor (like an air bladder) or other finicky gizmos to try and defeat these issues.  Did you know there is a simpler way yet, that also gives you greater control?  The most effective systems are open-ended and do not have floats.  When the end of a pipe is open, pressure waves cannot build up and reflect.  The problem with open-ended systems is, how do you know when the tank is full?  The secret: add an electronic water checker and well controller.  

 

Modern water pipelines use electronic controls to manage water demand.  A transducer sits at the end of the line, such as a Tank Toad, and measures the water level in the downstream tank.  When the water level drops to a preset threshold, the Tank Toad sends a signal back to the well house, and demands water from the well.  The well can start pumping.  Once the tank is filled, the Tank Toad sends another message back to the wellhead to stop the pump.  Not only is this system simpler from a mechanical standpoint, but you get the added benefit of knowing what the status is at both the tank and the pump.  You can track how many hours the pump has been running, as well as check the water level in the tank itself.  If you have a leak, you’ll know within a few hours, because you’ll receive an alert and can check up on the pump itself.  Simply adding two smart gizmos forms the core of a modern, efficient, and proactive water management system.  Give us a call and we can review your water system for free.