Speaking as someone old enough to remember those old galvanized tanks in the 60’s, they had LOTS of problems, which is the reason we switched to bladder style tanks. The air charge would always mix with the water and soon the tank was waterlogged. Then the pump would rapid cycle on and off for a few days before losing its fight with cancerous cycling. Pre-charging a galvanized tank would make it take a little longer, but does not solve the problem of losing air.
There is no “skill” in just throwing in whatever size tank the customer can afford and “hoping” to be lucky enough for the pump to survive millions of cycles. “Skill” comes from first understanding that cycling is the biggest killer of pumps and then knowing how to reduce or eliminate the destructive cycling. Cycling can destroy any pump. The larger the pump and the more long-term uses of water there are, the more destructive cycling becomes. Small pumps with no long-term uses of water can survive many cycles, but the fewer the cycles the longer any pump will last.
There are always trade-offs. The following is a list of options and there effects.
#1
Pressure tank too small to give at least 1 minute of run time.
Rapid cycling causes the shortest life for the pump, tank, check valve, pressure switch, relays, etc.. Causes frequent fluctuations in house pressure. Causes water hammer and other problems. The larger the pump and more long-term uses of water there are like irrigation, filling pools and ponds, the shorter the life of the pump and all related equipment.
#2
Pressure tank large enough to get at least 1 minute of run time.
Reduced cycling for short and long-term uses of water. Pressure fluctuations in the house will be more gradual, but will stay low for longer periods of time. Any long-term water uses will still cause repetitive cycling and greatly shorten the life of the pump and all pump equipment. Will get years of pump life when used only for home water supply, but greatly reduced pump life with long-term uses of water.
#3
Really small pressure tank with a CSV.
Cycling is completely eliminated for all long-term uses of water. The number of cycles for home use alone will be about the same as option #2. This is because the extra cycles for toilets and hand washing will be made up for by the elimination of cycles for longer term uses of water like showers and garden hose use. However, there will be less pressure fluctuation, as this system will provide “constant pressure” for almost every use of water. Will get many years of pump life for short and long-term uses of water.
#4
Larger pressure tank working with a CSV.
Cycles are completely eliminated for all long-term uses of water. Cycles for short-term uses like toilets and hand washing are reduced and equal to option #2. Pressure fluctuations will be more noticeable and have longer durations. This option will give the longest pump and equipment life possible for any type of water use. However, the added life of the pump will not justify the added expense and space needed for the larger tank.
A CSV with a small tank as in option #3 will be the lowest cost, save the most space, deliver the strongest constant pressure, and cause the pump to last at least as long as the old school large pressure tank only design.
In-rush currents and all the bad things that happen to a pump don’t just happen when rapid cycling, it happens for any cycling. So the fewer cycles the longer the pump will last, which is a well-known fact for those with any knowledge of how pumps work. Contrary to what some people “think”, these type pumps will last longer when running 24/7 even when only pumping 1 GPM than they will last with any amount of cycling.
