Waterco Half Barrel Union - 40mm - 122243B

Waterco Half Barrel Union - 40mm

Genuine Waterco 40mm half barrel union, comprising the threaded locking nut, the glue-in tail piece and the union O-ring. Waterco part number 122243B (also listed as 122243, WC122243B, 89-252-1100). This is the standard 40mm / 1½" union used across the smaller Waterco pumps, the 40mm multiport valves, and a number of Waterco filters.

• Physically Stocked, unlike most "drop-shipping" websites.
• Shipped from VIC, NSW, WA, QLD

What's Included

• 1 x threaded barrel union locking nut
• 1 x glue-in tail piece (solvent weld to 40mm PVC pressure pipe)
• 1 x union O-ring

Quick Size Check

This is the 40mm union. The glue socket accepts 40mm PVC pressure pipe, which has an actual outside diameter of around 48mm — not 40mm. If the pipe going into your existing union measures roughly 48mm across the outside, this is the correct size. If it measures around 60mm OD you have 50mm pipe and need the 50mm union instead. Measure the pipe, not the union nut.

Compatible Waterco Pumps

• Aquamite 50, 75, 100, 125
• Aquastream 50, 75, 100, 125, 150

Waterco list 122243B as the half union against these pumps on their own spare parts diagrams.

Compatible Waterco Filters, Valves & Equipment

• 40mm multiport valves — top mount and side mount
• Trimline C100 and CC150 cartridge filters — these two models use the 40mm half union rather than the 40/50mm unit fitted to the rest of the Trimline range
• Aquamite filters
• Hydron filters
• Waterco sand and cartridge filters supplied with 40mm ports

Will NOT Fit — Check Your Port Size First

Waterco uses a different union at every port size, and they are not interchangeable. If yours is not 40mm, you need one of these instead:

• 50mm — part 634024B. Click here for the Waterco 50mm half barrel union.
• 50mm x 40mm reducing — parts 122257BLK / 634024542, used where a 50mm port is plumbed down to 40mm pipe. This is also the union fitted to Trimline MkIII cartridge filters from 2001 onward.
• 65mm x 50mm — part 63406550BLK, used on Hydrostar 200–350, Hydrostorm Plus 300–400 and Supaflo
• 80mm — part 6340803, used on Hydrosteel and Hydrostar Commercial
• 100mm — part 6340801, used on large commercial filters and Hydron

Also not this part: Opal and Opal XL cartridge filters use their own union set (AXFI014 tail, AXFI016 lock ring, AXFI018 O-ring). Portapac and Aquastream Solar use the 50/40mm S13185A union.

Part Numbers & Search References

• 122243B (current Waterco part number)
• 122243
• WC122243B (Waterco USA reference)
• 89-252-1100
• Union O-ring only: 64479

Some older catalogues also list a 40mm half union under 122244. If that is the number on your paperwork, compare the nut thread and tail length against your existing union before ordering, or send us a photo and we will confirm it.

Common search terms: Waterco 40mm half union, Waterco barrel union 40mm, Waterco pump union kit, Aquamite union, Aquastream union, Hydron union, Waterco MPV 40mm union, 122243B, Waterco 1.5 inch half union with o-ring, Waterco pump tail piece and nut.

Understanding 40mm Nominal Sizing

In plumbing, named sizes are not measured sizes. A pipe called "40mm" or "1½ inch" does not measure 40mm across — it follows nominal sizing, an internationally standardised naming convention. 40mm PVC pressure pipe has an outside diameter of approximately 48mm. Always use the OD of the pipe to confirm the fitting size.

Fitting Notes

• Solvent weld the tail piece to 40mm PVC pressure pipe using an approved priming fluid and PVC cement. Allow full cure before pressurising.
• Seat the O-ring in the tail groove and lubricate with a silicone-based lubricant only. Petroleum jelly and mineral greases swell and destroy the rubber.
• Hand tighten the nut only. These unions seal on the O-ring face, not on thread compression. Multi-grips and pipe wrenches crack the nut and do not improve the seal.
• If a union weeps after tightening, the cause is almost always a nicked, flattened or dirty O-ring, or grit on the sealing face — not insufficient torque.
• Support the pump and pipework so the unions are not carrying pipe weight or misalignment. Side load is the most common cause of a cracked union nut.

Why Replace A Barrel Union?

• Cracked or split locking nut, usually from over-tightening or UV embrittlement
• Persistent weeping at the pump inlet or outlet
• Air being drawn in on the suction side, causing loss of prime or a pump that will not hold water
• Stripped or cross-threaded nut that will no longer pull up square
• Damaged tail piece sealing face
• Retrofitting a new pump onto existing pipework

A weeping union on the suction side is worth attending to promptly. It draws air rather than leaking water, so there is no puddle to warn you, and running a pump with entrained air will damage the mechanical seal.

Frequently Asked Questions

How many do I need?
Two for a complete pump changeover — one per port. One only if you are replacing a single failed side.

Does it include the O-ring?
Yes. The union O-ring (64479) is supplied with it. You can also buy that O-ring separately if the nut and tail are still sound.

How do I know I need the 40mm and not the 50mm?
Measure the outside diameter of the pipe entering the union. Around 48mm OD is 40mm pipe and takes this union. Around 60mm OD is 50mm pipe and takes part 634024B.

Will it fit my non-Waterco pump?
Only if that pump was built on a Waterco body. Other brands use their own thread forms — an Astralpool, Onga, Davey or Poolrite 40mm union is not interchangeable with this one even though the pipe size matches.

Can I use thread tape on it?
No. The seal is made by the O-ring against the port face. Tape on the barrel thread does nothing useful and can prevent the nut pulling up square.

Not Sure Which One You Need?

Send us a photo of your pump label and the existing union and we will confirm the correct part and quantity. Waterco has used at least six different union sizes across their range, and the wrong one is a wasted trip.

Manufacturer Catalogues, Diagrams & Part Numbers

Need exploded views, spare part numbers, product numbers, diagrams, or more product information? See the manufacturer catalogue: Waterco Catalogue 2026