High And Low Water Pressure Systems?

Before you go out and buy a new shower rose or tapware, there’s something’s you need to know.

Do you have a mains (high pressure) or a low pressure hot water system?

Figuring out which system you have is easy. Turn both the hot and cold taps over the basin on full. If the cold flows much faster than the hot, you have a low pressure hot water system also known as an unequal pressure system . If the flow of the hot and cold are about the same then you have a high pressure hot water system also known as a Mains Pressure system. Alternatively you can loot at the label on the hot water cylinder , more often than not it will be stated.

Low pressure 36 - 72 KPA  (average warm shower flow of 7 litres per minute)

Mains pressure 600 - 1100 KPA  (average warm shower flow of 12.5 litres per minute)           

Once you know what pressure system you have you are ready to go shopping. If you have a low pressure system you should be looking for ‘low or all pressure tapware. If you have a high pressure system you will be looking for ‘mains or all pressure tapware.

At Elite Bathroomware we will recommend the correct tapware to best suit your system you could also ask your plumber which tapware and shower roses he has found to be most effective in your specific situation.

Shower roses vary according to the system they’re designed for. If you fit a high pressure rose to a low pressure system, you will find you might have water flow issues and or you might get trouble finding a nice temperature mix.

Most new homes now have high pressure cylinders because of their significant advantages. You can run two showers at once without an appreciable drop in the flow of hot water, or do the dishes while someone is in the shower.

There are no disadvantages to a high pressure system apart from you will end up using slightly more hot water

Low pressure systems, however, can create a challenge with the new requirement for tempering valves to be installed between the cylinder and any new shower.

A low pressure system will be affected by the tempering valve because it effectively reduces the flow of the hot water. Home owners who are faced with replacing existing hot water cylinders are probably wise to opt for a new high pressure cylinder.

The water flow is greater on these cylinders and it is not a significantly any more expensive than a low pressure systems.

Basic Hot Water Cylinder facts

 Low Pressure Cylinders

The majority of Pre 1990 New Zealand homes have low pressure hot water systems. The cylinder is made of copper and is open-vented. The system comprises a thermostat, an element, a pressure reducing valve and possibly a vacuum valve. A vent pipe will either poke out of your roof, or over an outside gully-trap. A small amount of water dripping occasionally from this pipe is normal as the system vents pressure, but a constant drip or dribbling indicates a problem.

Low pressure pros and cons

• Advantages: they are cost-effective and can be used in conjunction with a wetback burner to cut power costs, if you use a "copper " low pressure cylinder, they will also be able to take much higher temperatures than 72C degrees ( lined cylinders) ,so you can store hot water at much higher temperatures. They also tend to use less hot water as the water pressure is much lower, which means the water comes out slower out of your shower for example, saving you water and & heating costs.                                                    
• Disadvantages: they won't give maximum performance in a shower unit and most modern or imported tapware require mains pressure hot water systems.
• An old cylinder will eventually leak and need to be replaced. Auckland’s water is not as hard as other cities around the world so you can reasonably expect to get 20-30 years from your cylinder. Keep a close eye on the floor around your cylinder as they can sometimes leak for months before being noticed, which causes considerable damage to the floor and results in high power bills.
• The valves will require occasional replacement of washers or diaphragms. If you see water coming out of the vent as described above, you will need to contact a plumber as this indicates a problem with the valve. The water that is being discharged has been heated and paid for by you. Seeing to the problem quickly will save you money.
• If the valve itself is quite old a plumber will normally replace the entire valve, rather than a washer or diaphragm. This is because they can’t guarantee the old valve and it is very likely to require attention again in the near future. It is therefore more cost-effective for you to replace the whole valve for around $200 - $250, than for a plumber to come out several times at your expense.
• The element may corrode inside the cylinder, resulting in a sudden loss of hot water.

Mains Pressure Cylinders

A mains pressure hot water cylinder is made of steel and runs at 600 - 1100 KPA . The cylinder is closed-vented, so you won’t find a vent pipe anywhere. The advantage of mains pressure is that water is delivered to the entire house at the same pressure, so it is less affected by multiple demands on water usage, such as simultaneous showers, running taps, washing machines etc.

The most common problems with a Mains Pressure hot water cylinder are valve-related.

• Pressure limiting valves can fail and allow too much pressure into the system, resulting in water continuously dribbling out of the expansion valve.
• Failure of the expansion or tempering valve will require replacements as there are no washers or diaphragms in these systems.