Water Pressure and Water Hammer: The Silent Pipe Killers

There’s usually a reason for burst pipes. Whether it’s a joint that’s split, or a hose that’s blown apart, you can bet two silent forces have been doing some overtime on your walls. Neither makes a smell or a noise before it strikes. And neither will trigger an alarm, either.

The first is water pressure. It never sleeps, it never takes the weekend off, and you can never turn it off. The second is water hammer – the sharp shockwave that slams through your pipes whenever a tap or valve is switched off. It’s the impact of that wave coming back that does the damage. When you combine the two of them, they account for almost every so-called “random” plumbing failure that occurs in homes across Sydney.

The good news: you can detect both of them yourself, and at a low cost using basic DIY skills. If left unchecked, however, either one can lead to a host of expensive repairs and significant property damage.

Here’s an insight into what’s actually happening behind your walls and what stops it.

Constant water pressure

The mains water is supplied to your home under pressure. Measured in kiloPascals (kPa), this pressure is how hard water is being forced against the walls of your pipes. That happens even when every tap in the house is closed off.

Think of it like your own blood pressure. A slight, consistent pressure is normal and necessary, but high pressure leads to wear and tear on the whole water system in your home over time.

The nature of Sydney’s hilly terrain makes the water pressure difficult to predict. Water pressure changes with height. A home situated lower down a hill in a specific supply zone will typically have higher water pressure than a property higher up the same street. That’s how gravity interacts with the mains water system.

For a new home, AS/NZS 3500 stipulates that the maximum water pressure is 500 kPa. Engineers specify that limit as a safe pressure that won’t cause strain for your pipes, fittings and appliances.

That only applies to new buildings though. Many of Sydney’s older homes have plumbing which was installed long before the standard was introduced, and have no pressure reducing valve fitted at all.

In the absence of a pressure reducing valve, it’s common for older homes to run at the same pressure as the main. This pressure then has to push against worn water pipes, fittings and joints. That leads to gradual but steady wear and damage that results in what looks like a plumbing issue.

If you recognise any of the following, you might have excessive water pressure in your system:

• Taps make a vibrating, or thumping, sound when you shut them off
• Washers and O-rings in taps need to be replaced much more frequently, often within just a few months
• A flexible hose bulges when the water is turned on, and bursts easily
• Your high-pressure shower head has enough power to take paint off a surface
• There are pinholes in your copper piping
• Inlet valves on appliances fail
• Minor, unexpected water leaks occur on fittings that normally never leak.

Ignoring these warning signs often allows minor wear to progress unnoticed, increasing the likelihood of sudden failures that could have been prevented with timely inspection and straightforward repairs.

These problems are not accidents. They are the direct consequence of repetitive strain applied to the pipework by high water pressure over many years, culminating in ruptured pipes or pipeline failure. Most homeowners will notice one or two of these symptoms long before they connect them with excessive water pressure. By the time several are occurring simultaneously, the system has likely been stressed for many years.

Water pressure can be checked cheaply and easily

You don’t need to call a professional plumber to find out what your water pressure is. You can purchase a water pressure gauge for about $20 from any hardware store. Simply screw it onto an outside tap.

Turn the tap on full and record the number shown. You should also check the pressure first thing in the morning before running any water-using appliances – this will give you your maximum reading for the day.

Your water pressure result:Installing a pressure reducing valve (PRV)

A PRV is one of a number of devices used to control water pressure. It’s a compact brass valve fitted on the main pipe just after your water meter. It limits the maximum water pressure delivered to all of your pipes and appliances to a safe level typically, 500 kPa. It essentially regulates flow, preventing full mains pressure from being distributed throughout your home system.

Installing a PRV is not a DIY job. It requires specific tools that are not generally owned by homeowners, and the positioning and calibration must be precise.

Fitting a PRV is a job that requires the services of a licensed plumber in NSW. If it is incorrectly installed or set, it can cause more problems with your water system than it fixes.

However, when correctly fitted, a PRV reduces stress on all of your pipes, hoses, and appliances. The result is a quieter system with no bulging hoses or thumping taps. It maintains optimal pressure for many years to come, with only occasional checks needed.

Water hammer: the noisy issue

While water pressure can silently wear down your pipes, water hammer is easily identified. It’s the sudden, loud bang, whump, or thud that resonates throughout your home when a tap or valve is turned off.

Moving water has significant momentum, and when a valve in a washing machine, for example, closes very rapidly, that momentum has to go somewhere. It produces a pressure surge which travels down the pipe as a wave of hydraulic shock, and strikes your pipes and their connections forcefully like a hammer blow.

Common sources of water hammer:

• Washing machines and dishwashers, which have solenoid valves
• Toilet fill valves
• Some irrigation controller valves
• Self-closing taps and single-lever mixers

A single spike may not cause a problem. But constant, repetitive strikes on the same pipe, fitting, or joint from a washing machine operating several times a week can build up over several years. That can lead to joint failure or rupture. If you have high mains water pressure already, the impact of a hammer blow is significantly magnified.

While most modern appliances can handle these daily shut offs, all the repeated closings eventually stress the pipes and fittings adjacent to the appliances. Older houses, with old pipes or poorly supported pipe runs, are particularly susceptible to shock and damage from an exposure to daily hydraulic shocks.

The clues from your pipes

A single, sharp noise when a tap or appliance switches off is likely to be water hammer. A persistent rattling or juddering noise when water is running, or an appliance is operating, is most likely a faulty washer or a fill valve that’s been put through the mill.

A low hum or constant whine may mean the water is running at too high a velocity, or that standing waves are set up within the pipes. A faint ticking or creaking sound after hot water has been running is likely simple expansion. But a loud, regular, metallic ticking could suggest the pipe has been clamped too tightly to move, and needs to be properly supported.

Noisy pipes are never just “the house settling”. They all have a specific cause, and most of them are inexpensive to remedy, if you know where to listen.

Regular inspections help detect problems before expensive plumbing failures occur.

Fixing water hammer

These are all proven solutions, and work best when used in combination.

Secure all of your loose piping and fittings.

If your pipework is unsupported, it vibrates and whips in response to pressure waves. That makes a lot of noise, and wears out everything. Supporting your piping with pipe straps, pipe clips and pipe brackets is the first step.

Install water hammer arrestors.

Small, sealed arrestors can be fitted near your washing machine. They work with a trapped cushion of air, stopping shock waves before they reach your wider network. This is the modern, virtually maintenance-free equivalent of old-style air chambers, minus the waterlogging.

Reduce the pressure.

The valve on the inlet pipe, located shortly after the water meter, reduces the overall system pressure throughout the house. Lowering static pressure leads to slower water flow and softer hammer blows across all of your pipes.

Service anything that flutters.

Worn or failing washers and valves not only cause water hammer, but are often its source. But they are usually cheap and simple to replace.

Add flexibility wherever you can

Expansion joints and gasketed joints allow your pipes to move with temperature changes, reducing stress on fittings and fixed connections.

Old air chambers used to be fitted for the same purpose as arrestors now serve. But modern air chamber installations and their tendency to become waterlogged have made purpose-built arrestors a much more popular and reliable choice for shock suppression.

Frequently Asked Questions

1. My water pressure feels really good. Is this a positive thing?

In short, not always. Higher static pressure is hard on every part of your system, including pipe joints and valves. They will degrade much faster, meaning you’re at greater risk of leaks and bursting pipes.

2. Does installing a pressure-reducing valve require professional plumbing work?

Yes, in NSW it must be performed by a licensed plumber, as its placement relative to your water meter affects performance.

3. I recently started hearing noises in my pipes. Why now?

If your pipes have suddenly become noisy, it usually means that something has changed. Perhaps a new appliance with a quick-closing valve has been installed, an old washer is nearing its end, a pipe clip has come loose, or the network water pressure has fluctuated. Often, water hammer is a sign that a part is about to fail, perhaps with a leak.

4. I’m a tenant. Who’s responsible for fixing the noise?

The homeowner or landlord is always responsible for maintaining your home in good working order. If your pipes are repeatedly making noise, especially due to failing washers and hoses, it’s best to notify your landlord in writing.

You just need a simple, clear explanation of what’s going on and when it happens. If it’s an ongoing problem, you’ll have documentation, and if plumbing repair becomes necessary, you can refer back to it.

The bottom line

Your house’s water pressure sends a steady stream of water through your pipes every day. On top of that, thousands of jarring water hammer impacts strike your pipes across the year. Combine those two factors, and it’s not difficult to see how even “sudden” pipe bursts could be predicted years in advance.

Even a cheap pressure gauge can tell you almost all that you need to know. The first step is always to listen to what your home is trying to tell you. From there, support straps for your pipes, water hammer arrestors for your appliances, and perhaps a pressure-reducing valve give you overall peace of mind.

It’s not a complicated or expensive process. Most repairs and fittings take a few hours, and costs only a fraction of what would be spent calling a plumber in for a 2am emergency. A small preventative measure can save you thousands, and avoid inconvenient pipe damage for years to come.

Premium Sydney Plumbers regularly undertake exactly this type of service across Sydney, fitting, testing and servicing pipes to eliminate noise and protect your home plumbing system long term. If your tap feels “thumpy,” the pressure seems excessively high, or you’d prefer not to take chances, call us today for a professional consultation.