Gravity Assist vs Pressure Assist

There are lots of ways to slice and dice toilet types – single-flush vs dual-flush, one-piece or two-piece or wall-mount, and so on. One other way is possibly, in a sense, the least interesting: flushing mechanism – gravity feed versus pressure assist.

I say “least interesting” because, as a buyer, why should you care about how the thing works inside? You only care whether your toilet works well and reliably for a long time. Well, it turns out that wanting to satisfy those criteria does, in fact, lead naturally to exploring the inside of the toilet.

First, some definitions…

Gravity-Assisted Toilets

Gravity-feed toilets are the type everyone is familiar with. They’ve been the mainstay of home waste disposal for generations. You push the handle that opens a valve inside the tank and gravity forces water to fall. When it falls inside the bowl a siphoning effect is created in the trapway (the “tunnel” at the base of the toilet). That siphoning action moves both water and waste down through the pipe into your septic tank or utility’s sewer pipes.

The tank then refills via a small gushing pipe (usually plastic) until a float shuts off the flow. If any water does happen to flow a little higher (from gushing, hand-motion inside, an earthquake, or whatever), there’s a narrow overflow tube to handle that. Thus, no spilling of water outside the porcelain tank.

Simple, effective, and long-lasting.

Pressure-Assisted Toilets

By contrast, a pressure-feed toilet houses an ‘active’ rather than merely passive mechanism. To the force of gravity it adds pressure created by a device that supplies even more force than the traditional unit. In the usual design, water displaces air inside a sealed cylindrical tank inside the larger ceramic tank, helping generate that larger force. Usually the cylinder is made of metal or plastic.

Pressure-assist toilets are far less common, even today, than the traditional design but becoming more popular all the time. The reasons why will be covered in later sections detailing some of the pros and cons of the two types. For now, it’s enough to say that just because the technology is newer it doesn’t necessarily follow that this type of toilet works better for you. Sometimes yes, sometimes no. Let’s see why.

Which Type Is Better?

It won’t surprise you to learn that there’s no cut-and-dried answer to the question posed in the section heading. Gravity-feed toilets are better in one way, not as good in others – and the converse is true of pressure-assist units.

Naturally, that vague answer is useless as a guide to potential buyers so let’s jump right in and see just how the two differ in detail and what advantages and disadvantages each design offers.

Gravity-Assist Toilets – Pros and Cons

One of the biggest advantages a gravity-feed toilet has is sheer longevity. By that I don’t mean here that they last a long time, though they do. I mean they’ve been around a long time. Theoretical design is one thing; real-world testing is another and no design has been in use longer or more successfully.

Sure, gravity-feed toilets go bad once in a while. But it’s usually something like the flap on the hole at the bottom no longer sealing perfectly. Often that happens because of something simple like mold accumulation and therefore repairable for free just by cleaning.

Sometimes the flush mechanism will misbehave. That, too, can be repaired by any semi-competent do-it-yourselfer for a small amount of money. On rare occasions a leak will develop around the base or in the hoses, requiring replacement of the seal or hose, but that’s almost never a failure of the toilet itself.

These things simply don’t break down very often, in part because they are so simple. The technology used to shape them and the parts that go inside has been around for decades. The components are durable and (when something does go wrong) usually cheap and easy to fix. About the only exception to that is the odd time when the lid cracks, but that’s almost always “user error”. Drop one too hard after an inspection of the tank interior and it can crack; that’s the nature of ceramics.

However, despite their obvious advantages, there are some drawbacks to a gravity-feed toilet.

As discussed, the flap, the float, and other parts inside don’t often go bad but they also don’t offer any “value add” to the design’s intent. That is, they don’t help remove waste. They’re all passive mechanisms, or parts thereof.

As a result, whatever pressure the toilet provides to remove waste is generated solely by gravity and sometimes that just isn’t enough. For large families or for individuals who use a lot of toilet paper, the gravity-feed toilet simply might not get the job done effectively.

Sure, we all know you’re not supposed to put feminine napkins and other items down the toilet. And, some of us have had times when a young child decides to “experiment” by seeing if Dad’s golf balls will go down the toilet. But, even apart from these “accidents”, there are simply some personal circumstances when the traditional design can’t supply enough oomph.

That can be the result of too many people using one toilet. It can result from age. Sometimes, the problem is outside the toilet entirely, such as partial blockage in the pipes. That’s more likely for those who live in ultra-cold winter environments where ice can form overnight inside the pipe, for example. Whatever the underlying cause, there are times when the weight of water and siphoning produced by the force of gravity simply isn’t enough pressure to dispose of the waste.

Pressure-Assist Toilets – Pros and Cons

That last con of a gravity-feed toilet leads directly to one of the pros of the pressure-assist design, and one of the major reasons they exist. A pressure-assist toilet provides a lot – I mean a lot – of pressure.

If you’ve seen videos of a good one in action you probably won’t believe it at first. These things can handle a small bucket of golf balls. They can force down a dozen short rubber tubes. They can flush 40-feet of wet toilet paper in one go. You just know they’re not going to have trouble with ordinary solid waste.

But that pro actually comes with a couple of inherent (potential) cons attached.

One is that, in order to generate that pressure, your home water system has to supply a certain amount of pressure to start with. The mechanism inside isn’t electric or mechanical. That is, there’s no motor or pump that builds up pressure waiting to be released when you flush. It just retains what’s available and lets it go at the right moment. As a result, your home water supply has to generate at least 25 psi (pounds per square inch) before a pressure-assist toilet will operate properly.

You can test that easily using a gauge you can obtain off the web or at certain hardware stores. They’re not terribly expensive (around $10, as of this writing) and not particularly hard to find. But not everyone is going to want to take even this relatively simple step when considering a toilet purchase.

If you’re paying for installation the plumber will undoubtedly have one in his toolkit. If you’re doing the do-it-yourself route you might not want to bother. So be it. Every purchase decision involves tradeoffs and toilets are no exception.

The other inherent drawback is the impact that high pressure can have on your water pipes. For those with newer homes it’s very unlikely to be relevant in your situation. There’s plenty of ‘headroom’ incorporated in the specs for home water pipes. But pipes do gradually age and weaken. Older, corroded pipes are like the arteries of some elderly people or old inner tubes. They sometimes get spots that are a little weak. With a bit of excess pressure they can pop a hole and leak.

That’s not likely even in older homes under most circumstances. But for those who live in very cold climates, where ice can build up inside in winter, the combination can tip you over the edge. If you’re interested in a pressure-assist toilet but are in that situation, the best thing to do is consult a plumbing professional and have your pipes evaluated.

One other drawback of a pressure-assist model has to do with its inherent design but not one that relates to safety; it’s just an issue of “user friendliness”. Most, if not all, pressure-assist toilets are loud – or, at least, a lot louder than the traditional gravity-feed unit. There are some models on the market that are much quieter than others but even they are louder than the equivalent gravity-feed design.

For those who are a little harder of hearing that might not matter. On the other hand, I’m getting a little in that direction myself and I always find the noise a little startling, even when I’m expecting it. After testing one for a time I still jump a bit when I push the handle and hear that ‘jet-passing-by’ sound. The noise is not enough to dissuade me from purchasing a pressure-assist model but these things are always personal. Let your sensitivity-level be your guide.

One interesting aspect of the pressure-assist design that can be a pro or a con (or neither) depends in part on your point of view. If you look inside, you’ll see no freestanding water. That bothers some people, probably just because they’re used to the traditional tank on a gravity-feed unit.

Personally, I see that as a benefit. It means there’s less to provide a growth environment for mold and mildew. That means a healthier environment for my family and less to clean or disinfect. It also means a tiny bit of savings on cleaning products, a nice little side benefit. Small potatoes in both cases, but every little bit helps when trying to decide between a gravity-feed toilet and a pressure-assist design.

Summing Up

Like anything, in the end only you can decide which toilet design – gravity-feed or pressure-assist – will work best in your circumstances. Narrowing the choice is made simpler if you ask yourself a few relevant questions:

What’s your budget? Pressure-assist toilets are usually more expensive. As a secondary question, can your home handle a new pressure-assist model without replacing the pipes? That’s both an issue of budget and potential hassle. Replacing pipes will usually have your home’s water system out of commission for a day or several.

What’s the average expected lifetime of the pressure-assist model you are considering? You know already that a good gravity-feed model will last for decades with little or no maintenance.

What’s your average usage “style”? Do you have a large family or many guests, or someone who needs to use a lot of toilet paper? Do you really need the extra oomph only a pressure-assist model can supply?

Once you answer these you’ll come quickly to a conclusion about whether your new toilet should be a gravity-feed model or pressure-assist. Keep in mind, whatever type you choose both are available in a wide range of styles and colors from many different manufacturers.

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