Well Tanks

Size by drawdown against your pump's flow rate. Pumps up to 10 GPM want roughly 1 gallon of drawdown per GPM of pump flow; 10 to 20 GPM pumps want about 1.5 per GPM; 20+ GPM pumps want 2 per GPM. In practice: a 1-2 bath home on a small pump fits a 20 gal tank (6.2 gal drawdown), the typical 2-3 bath home fits the 32 gal WX-203 (9.9 gal), and 3+ bath homes or high-flow pumps step up to the 44 gal WX-250 (13.6 gal) or the 87 gal WM25-WB (26.8 gal). When in doubt, go bigger: more drawdown means fewer pump starts.

Just under your pump's cut-in pressure, set with the tank empty. The two brands use different rules: Amtrol Well-X-Trol tanks get cut-in minus 2 PSI (the factory ships them at 38 psig for a 40/60 switch), and Pentair WellMate tanks get cut-in minus 4 PSI (26 psig on a 30/50 system, 36 psig on 40/60). Check it with a tire gauge at the schrader valve with the water drained, and re-check yearly.

Usually the tank: a lost air charge or an undersized tank. When the diaphragm or bladder fails, water displaces the air cushion and the pump fires every few seconds (a waterlogged tank thuds full top to bottom instead of ringing hollow up top). A faulty pressure switch or clogged lines can do it too, but the tank is the first suspect. Short cycling is worth fixing fast, because frequent starts are what burn out pump motors.

40/60 gives stronger house pressure; 30/50 gives more drawdown. The same tank delivers less usable water at the higher setting: a WX-203 yields 9.9 gallons at 30/50 but 8.6 gallons at 40/60. If your home has multi-head showers or runs fixtures on a second floor, 40/60 is usually worth it; just size the tank for the drawdown at that setting and match the pre-charge to the cut-in you actually run.

Until the air charge can no longer be held: there is no rebuilding one. Lifespan depends on cycling frequency (a right-sized tank cycles less and lasts longer), pre-charge maintenance, and corrosion. Amtrol backs the Well-X-Trol line with a 7 year limited warranty and Pentair backs WellMate composites with 5 years. In damp or coastal spaces, fiberglass composite tanks remove shell corrosion from the equation entirely; the WellMate shell cannot rust.

Because most of the tank is the air spring. A captive-air tank is split by a diaphragm: compressed air above, water below. The air has to occupy enough volume to push the water out across the full pressure band, so only a fraction of the label volume comes out between pump cycles. That usable fraction is the drawdown, and it is the only number that sizes a tank: 6.2 gallons on a 20 gal WX-202, 9.9 on a 32 gal WX-203, 13.6 on a 44 gal WX-250, all at a 30/50 switch (Amtrol's own spec card figures).

This is also why running a 40/60 switch costs you water: the same WX-203 drops from 9.9 to 8.6 gallons because the air spring works across a higher, narrower band. We publish the manufacturer catalog drawdown on every tank we sell so you are never sizing from a label number.

Steel Amtrol Well-X-Trol tanks are the default: 150 psig rated, a 7 year warranty, and every package ships with the complete brass tee kit. If your tank lives in a dry basement or utility room, steel is the proven, economical pick and it is what most plumbers install.

Fiberglass composite WellMate tanks win in hostile environments: a continuous-strand fiberglass shell over a seamless polyethylene liner cannot rust, inside or out. Damp basements, humid crawlspaces, coastal air, and high-iron water all eat steel shells from one side or the other. If this is the second steel tank the space has killed, the WellMate is the last tank that space will need. Trade-offs: 125 psig rating instead of 150, a 5 year warranty instead of 7, and the tanks ship bare (your plumber reuses the existing tee hardware).

A true captive-air tank, no. Waterlogged means the diaphragm or bladder has torn and water has taken over the air side. Adding air through the schrader valve buys days at best, because the air now dissolves into the water through the tear, exactly the failure mode the diaphragm exists to prevent. The tank gets replaced.

Worth knowing before you condemn the tank: a healthy tank that has simply lost some pre-charge CAN be recharged. Drain the system, check the air at the schrader valve with a tire gauge, and set it to the brand rule (Amtrol: cut-in minus 2 PSI, WellMate: cut-in minus 4 PSI). If it holds for months, it was just maintenance. If the pump is short-cycling again within days, the diaphragm is gone, and the fast knock test confirms it: hollow ring up top is healthy, a dull thud means water where air should be.

They solve a different complaint. A standard tank system swings between cut-in and cut-out (30 to 50 PSI, say), and some people feel that swing in the shower. A constant-pressure system modulates the pump to hold one steady, city-like pressure using a small tank. Customers who switch describe the difference as night and day, but it is a premium answer to the pressure-swing complaint, not to short-cycling.

If your complaint is the pump machine-gunning on and off, a correctly sized standard tank fixes it for a fraction of the cost. If your complaint is pressure that wanders while you shower and you want it flat at all times, ask us about constant-pressure options. Tell Aidan which symptom you actually have and he will point you at the cheaper correct fix.

The tank plus the complete TFP3-RV brass tee kit: the tee itself, the pressure switch, the pressure gauge, the relief valve, and the drain fitting. That is every part that lives at the base of a pressure tank, which means your plumber plumbs it in without a single parts run. Bare tanks from marketplaces and big-box stores leave you sourcing those five parts separately, and the install stalls when one of them is not on the truck.

WellMate fiberglass tanks ship as bare tanks (1 in male NPT on the WM-6 and WM-12, 1-1/4 in on the WM25-WB); on a like-for-like swap your plumber typically reuses the existing tee hardware if it is in good shape, or adds a new kit.

First. Water flows from the well pump to the pressure tank, then to everything else: sediment filter, iron or sulfur filter, softener, acid neutralizer, UV. Treatment equipment placed ahead of the tank throttles the pump and takes pump-cycle pressure spikes it was never designed to absorb, so the tank always anchors the front of the train.

One exception lives in this collection and it is not a pressure tank at all: a retention tank (like the WellMate UT120) goes downstream wherever chlorine, peroxide, or soda ash is injected, to give the chemical contact time before the water reaches the filters and the house. If you are building a full treatment train, send us your layout and we will map the order for free.