InspectAPedia ® | ||||||||||||||||||||||||||
| Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice |
| |||||||||||||||||||||||||
| InspectAPedia Home |
| | Air Conditioning |
| | Electrical | | | Indoor Environment |
| | Exteriors | | | Heating | | | Home Inspection |
| | Insulate Ventilate |
| | Interiors | | | Mold Inspect/Test |
| | Plumbing Water Septic |
| | Roofing | | | Structure | | | Contact Us |
| Directory of Professionals to Inspect or Test a Building | ||||||||||||||||||||||||||
|
PLUMBING TOPICS OIL TANKS SEPTIC SYSTEMS WATER PRESSURE REPAIR GUIDE & COSTS WATER PRESSURE & FLOW MEASUREMENT WATER PRESSURE LOSS DIAGNOSIS GUIDE WATER PRESSURE & FLOW MEASUREMENT WATER PUMPS & WELL TANKS WATER PUMP CONTROLS & SWITCHES PUMP TYPES & LIFE EXPECTANCY WATER PUMP, ONE LINE JET PUMP, TWO LINE JET PUMP, SUBMERSIBLE WATER PUMP & TANK SAFETY WATER SUPPLY & DRAIN PIPING WATER TANK TYPES: WATER, OIL, EXPANSION, ALL CAPTIVE AIR BLADDER WATER TANKS STEEL WATER TANKS BIG WATER STORAGE TANKS OPEN WATER TANKS WATER TANK LIFE EXPECTANCY WATER TANK REPAIRS CONTROLS & SWITCHES on WATER TANKS WATER PUMP SHORT CYCLING SHORT CYCLING DETECTION SHORT CYCLING CAUSES WATER TANK AIR, HOW TO ADD WATER TANK AIR LOSS SIGNS WATER TANK REPLACEMENT WATER TANK BLADDER PRESSURE ADJUSTMENT WATER TANK PRESSURE CALCULATIONS WATER TANK SIZE & VOLUME WATER TANKS HOW THEY WORK WATER TESTING WATER TREATMENT EQUIPMENT CHOICES WELLS CISTERNS & SPRINGS Basement Wells Cisterns Drilled Wells - steel casings Driven Point Wells How Much Water is In the Well? How to Test Well Water Quantity How to Get More Water From a Well Hand Dug Wells Springs as Water Supply Well Pits More Information InspectAPedia Blog - News Updates Air Conditioning & Heat Pumps Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure Accuracy & Privacy Policies Contact Us |
How to Find Out How Much Water is in the Water Tank, Considering the Space Taken up by Air in a Water Pressure TankIt's not how much water the tank holds that is useful to know. It's how much water we can get out of the water tank before the pump has to turn on. This is the "draw down" volume, which we can measure or calculate, or we can focus instead on how long (in time) we can run the water before the pump has to turn on. (See our discussion of "short cycling" water pumps at Water Tank Repairs: Diagnose "Water Pump Short Cycling" & Restore Air in a Building Water Tank. If your pump is short cycling you want to fix it, as we explain in that article. How to calculate the volume of water in a water tank
For the 36" diameter x 99" long water tank above, we calculated the water tank volume as follows: [3.1416 x (18")2 x 99" = 100,782 cu.in.] / 231 = 436 gallons in this water tank. That's a big tank storing a lot of water, probably indicating a well with a very low flow rate at the home where this water tank was installed. Or someone was planning to survive a long dry period. The small control connection shown at the 11 o'clock position on the end of this water tank was an air volume control. Domed water tank volume: If we needed to be precise and if the bottom and top of a water tank are domed at the top and convex at the bottom (usually) we can measure these areas and calculate their volume using the formula for the volume of a sphere (or part of one). But we suggest skipping this detail. Probably the spherical volume lost from the convex tank bottom is about equal to the spherical volume of the tank top, so it's a wash and we can just use the tank's overall height and diameter. A 30 gallon water tank does not give you 30 gallons before the pump turns onRemember that a "30 gallon water tank" used to control water pressure and pump cycling in a building does not hold 30 gallons of water, but something less than that (say 20 gallons of water max and 10 gallons of air at the point of pump cut-off). Then as you draw water out (and the in-tank pressure falls down to the pump cut-on point) the pump is going to come on before all of the water leaves the tank. So the maximum actual water you get out of the tank is less than the tank size, maybe 15 to 20 gallons max. The bladder-type pressure tank manufacturers cite an "equivalent" draw-down water volume as that provided by the older bladderless tanks. How to measure the draw-down water volume provided by a water tank
What are some typical water tank draw down volumes?A 10 gallon water pressure tank that starts fully empty and is pumped up to about 50 psi will contain about 3 gallons of air and 7 gallons of water. The water tank in normal operation does not draw down to 0 gauge pressure before the pump comes on. The water tank provides out flowing water down to 20 psi (on a 20-40 psi system or down to 30 at a 30-50 psi system) when the pump comes on. A water pressure tank with a total volume of 10 gallons and operating between 20 psi and 50 psi of pressure will have a draw down water volume of just 4.35 gallons of water. A typical kitchen water faucet runs between 3 gpm and 5 gpm (varying as the water pressure in the system varies as the water pump cycles on and off), so we can expect to run the water at the tap for about a minute before the pump will come on with this theoretical water tank. Because the pressure drops as the water tank empties and then increases as the water pump comes back on, the water pressure at a faucet or other plumbing fixture will vary between the pump cut-in pressure (typically 20 psi or 30 psi) and the pump cut out cycle (typically 40 psi to 50 psi). quoting from Water Tank Pressure, Temperature, and Air Volume Calculations. The above-cited article, which we admit is a bit unnecessarily complex (I was answering someone else's query) has the math you need to calculate the actual draw-down volume of water you get with a given sized tank, with a given in-tank water volume when the pump has reached its shutoff point. ... Technical Reviewers & References
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. PLUMBING TOPICS
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
| ||||||
|
PLUMBING TOPICS WATER PRESSURE REPAIR GUIDE & COSTS WATER PRESSURE & FLOW MEASUREMENT WATER PRESSURE LOSS DIAGNOSIS GUIDE WELLS CISTERNS & SPRINGS More Information InspectAPedia® Home & Site Map Air Conditioning Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure Accuracy & Privacy Policies Contact Us |
More Information about Plumbing and General Building or Home Inspections
|
11/03/2009 - 01/03/2008 - InspectAPedia.com/water/WaterTankSiz.htm - © 2009 - 1988 Copyright Daniel Friedman All Rights Reserved - InspectAPedia® is a Registered U.S. Trademark