Promax offers two types of aboveground water tanks: the premium ENDURO tanks and the more budget-friendly XPRESS tanks. They share most of their engineering, the same plastic and the same factory. The one difference that drives everything else, including what you are able to do with the tank once it is on site, is the sidewall.
The difference is in the sidewall
The main difference between the two is the strength of the sidewalls. The ENDURO tanks have corrugated sidewalls, which make them much stronger than the smooth wall of the XPRESS tanks. Corrugation is a shape doing the work of extra material. A profiled wall resists deflection in a way a flat wall of the same plastic cannot, so the ENDURO carries load through its geometry rather than through sheer thickness. That single decision is what separates the two ranges on burial depth, backfill and earthquake behaviour, rather than any difference in the material itself.
What the Kaikoura earthquake showed
This difference in strength is evident in the aftermath of the Kaikoura earthquake. The ENDURO tanks were able to withstand the shaking without any damage, while many other tanks were destroyed. This is because the corrugated side walls of the ENDURO tanks have much more inherent strength than a flat wall, so could better withstand the quake. A quake loads a full tank in precisely the way a flat wall handles worst: the water moves, the wall has to take it, and a shape that resists deflection has the advantage. You can read more in which is the strongest water tank, and on what a seismic restraint does.
Burying an ENDURO
ENDURO tanks can be inset in the ground up to 1 metre** and still retain their 20-year warranty*. This makes them a great option for those who want to keep their tanks out of sight, or who need to lower the tank to achieve fall in the downpipes. Fall is the reason this feature earns its keep on real sites, because the tank inlet has to sit below the gutter and on a flat site the only direction available is down. The warranty surviving the burial is the part that matters. There are more reasons to choose an ENDURO, but this is the one that changes site layouts.
The flat spot below the manway
Our ENDURO tanks also have a bonus feature, and it only makes sense once you have tried to plumb a sunken tank. On the ENDURO there is a flat spot on the sidewall 1 metre up from the base and directly below the manway. So if you do inset the tank in the ground 1 metre**, that flat spot arrives at ground level and you can still have your pipework accessible where you can reach it. Without it, insetting a tank means burying your fittings along with it, and every future connection or repair turns into an excavation.
Where XPRESS makes sense
The XPRESS tanks are also a good option. While they do not have the same advantages as the ENDURO tanks, like all Promax tanks they are designed and engineered without compromise and their long-term structural integrity is assured. XPRESS tanks boast a simple and streamlined design, are available in two colours, and come with a budget friendly price. If the tank is going onto a prepared base above ground and staying there, the corrugated sidewall is buying capability you will never call on, and the XPRESS is the sensible tank to specify. Getting the base right matters more in that case than the sidewall does.
What both tanks share
Most of the specification is common to both ranges, which is why the choice comes down to the sidewall rather than to a long list of trade-offs:
- Heavy ribbed roof design makes the roof strong
- 600mm dia manway is the largest and strongest on the market (15,000, 25,000 and 30,000 LTR models)
- Self-vented manway lid, with venting capacity of up to 1x 100mm inlet
- Multiple plumb points all around the tank
- Premium grade plastic, manufactured in house
- UV Stabilised
- Built to AS/NZS 4766
- 20-year warranty*
Both ranges are built to AS/NZS 4766 and both carry the 20-year warranty*, so the XPRESS is not a lesser tank in the way a cheaper tank usually is.
ENDURO vs XPRESS at a glance
Four things separate the ranges, and all of them follow from the sidewall:
- Sidewall construction: ENDURO corrugated, XPRESS smooth
- Strength levels: ENDURO maximum, XPRESS standard
- Burial depth: ENDURO up to 1 metre**, XPRESS cannot be buried
- Colour options: ENDURO 7, XPRESS 2
Burial depth is the line that most often decides it. An XPRESS tank cannot be buried, so if the site needs the tank lowered then the choice has already been made for you, whatever the budget says. Colour is the only difference on this list that is about how the tank looks rather than what it can do.
So which tank is right for you?
The best tank for you will depend on your specific needs and budget. If you need a strong tank that can be buried, the Promax ENDURO is a great choice. If you are on a budget, and do not require the tank to be buried, the Promax XPRESS is a good option. In practice the decision resolves itself once you know the site. Burial, backfill or an awkward position points to ENDURO; a straightforward aboveground install on a good base points to XPRESS. Call Promax on 0800 77 66 29, or contact the team and we would be happy to help you choose.
*(10,000 LTR and above)
** ENDURO Tanks 5,000L and smaller can be buried 1/3 of their height.