The WellMate WM-9 is a composite pre-pressurized captive-air tank for residential, light-commercial and pressure-boosting duty. The one-piece seamless inner shell is moulded from high-density polyethylene and wound in continuous fiberglass, so there is nothing in the vessel to rust — which is what makes these tanks the usual choice in agricultural, livestock and coastal installations where a steel tank corrodes.
Specifications
| WellMate WM-9 — Pentair WM900 (09-01-23) | |
|---|---|
| Capacity and performance | |
| Tank volume | 29.5 gallons (112 litres) |
| Drawdown at 30/50 psi setting | 9.1 gallons (34.4 litres) |
| Maximum operating pressure | 125 psi (862 kPa / 8.6 bar) |
| Dimensions and connection | |
| Diameter | 16 in (41 cm) |
| Overall height | 44 in (112 cm) |
| Height, inlet to floor | 1.75 in (4.4 cm) |
| System connection | 1" MNPT |
| Weight | 27 lb (12.2 kg) |
| Operating temperature | |
| Maximum external | 120 °F (49 °C) |
| Maximum internal | 100 °F (38 °C) |
| Minimum | 40 °F (4 °C) |
| Identification | |
| Model (domestic / international) | WM-9 / WM0120 |
| Pentair catalog number | 34719 (Quick Connect) · CH30854 (Classic) |
How it is built
- Interior air cell of heavy-gauge engineered polymer, fully replaceable.
- Inner shell — one piece, seamless, moulded high-density polyethylene.
- Outer shell — continuous fiberglass strands sealed with high-grade epoxy resin.
- Base — sturdy moulded polymeric, corrosion- and impact-proof.
- Bottom inlet/outlet — quick-connect assembly moulded in high-impact engineered polymer (Classic style uses a one-piece high-impact PVC drain).
Drawdown, not tank volume, is what sizes a pressure tank. At a 30/50 psi switch setting the WM-9 delivers 9.1 gallons per pump cycle from its 29.5-gallon body. Drawdown falls as the switch setting rises, so confirm the figure against your own cut-in/cut-out pressures before selecting.
Why composite rather than steel
Corrosion-proof construction, lighter weight and simpler service. A WM-9 weighs 27 lb, so it is usually a one-person installation with fewer man-hours than an equivalent steel tank, and the replaceable air cell means the vessel can be serviced in the field rather than replaced. Greater drawdown than a comparably sized steel tank also means fewer pump starts for the same delivered volume.
Need help sizing a tank to your pump and pressure switch? Contact our engineers.
Source: Pentair “WM900 (09-01-23)” WM Series Captive Air Tanks data sheet. Diameter, height and weight may vary slightly without notice, per Pentair. Drawdown figures follow Boyle’s law per current industry standards; actual drawdown varies with pressure-switch accuracy and system temperature. Pentair and WellMate are trademarks of Pentair plc, used here to identify the product supplied. Confirm all critical figures with ForeverPure before purchase.
