Pentax 3S 3-Inch Multistage Borehole Pumps

Where to Use Pentax 3S Borehole Pumps

The 3S range suits small private water supplies from a narrow borehole: feeding a house, cottage or holiday let through a pressure vessel or header tank, watering a garden or smallholding, and topping up storage tanks from a bore some distance below ground. Our guide to selecting the right well and borehole pump walks through the wider choice.

Size the pump on head at your working flow, not on the maximum figures. At 20 l/min the 3S 3-15 still gives about 36 metres of head and the 3S 3-30 about 73 metres, but at the full 45 l/min those fall to 7 and 17 metres. Our guides to pump head and flow rate and calculating pump size show how to work out your figure.

Pentax rates the range for clean water with no more than 40 g/m³ of sand, and its manual asks for the pump to sit below the pumping water level and clear of the bottom of the well. The pump must never run dry, so Pentax recommends level probes that switch it off automatically if the water drops. Wire it through a control panel with an isolator and short-circuit and overload protection rated to the motor nameplate. In a bore much wider than the pump, fit a cooling jacket so water passes the motor at 0.1 m/s or more. For bigger flows from a wider well, see the Pentair Dominator 5″ well pumps or browse all well and borehole pumps.

Frequently Asked Questions

Will a Pentax 3S fit my borehole?

Pentax designs the 3S for 3-inch wells. Measure the internal diameter and check the bore is straight and clear down to your setting depth. If your bore is 4 inches or wider, a 4-inch pump will usually give you more flow, and in a much wider bore a 3S needs a cooling jacket.

What do the numbers in 3S 3-15, 3-23, 3-30 and 3-45 mean?

The last number is the number of impellers in the pump end. The 3S 3-15 has 15 and the 3S 3-45 has 45. More impellers means more head at the same flow, so maximum head climbs from 46 to 128 metres while maximum flow stays at 45 l/min.

Can I run the 3S 3-45 on a single-phase supply?

Not the model we stock. The 3S 3-45 (code 022-926) is a 400v three-phase pump. The highest-head single-phase model in the range is the Pentax 3S 3-30, at 92 metres maximum. Call us if you need more than that on single-phase.

How much water will a 3S pump deliver?

Up to 45 litres per minute, but only at low head. At 30 l/min the four models give about 28, 43, 57 and 75 metres of head respectively. Work out your total head first, then read your flow from the curve on each product page.

Does a 3S pump need a control panel or protection?

Yes. Pentax’s manual calls for the supply to run through a control panel with an isolator, short-circuit protection and overload protection rated to the nameplate current, and recommends level probes to stop the pump running dry. Ask us what control gear comes with the model you choose, and for drop cable and jointing to suit your depth.

For help choosing a 3S model, call the AES Rewinds team on 01252 515169 or email sales@aesrewinds.com. If you need a submersible well pump for an open well or tank rather than a narrow bore, the JS-530 Well Buddy multi-stage pumps are worth a look.