Do I Need My Head Examined?

By Tom Neale
Illustrations By Mirto Art Studio

No one wants to deal with a broken or clogged toilet, but understanding the basics can help you fix it.

Heads are hated when they do us dirty. No one wants to deal with them, but sometimes you've got no choice. Knowing the fundamentals of how each type of head operates can help you fix one more easily or, better still, get someone else to fix it. Here are some of the commonly used types of heads and how they work — or don't. This article isn't exhaustive, but it should give you a head (ahem!) start on diagnosing your problem.

Double-Action Piston Pump

The Raritan PH II (which I've used since it was introduced) is a good example of a repairable, double-action piston pump. It can be powered by hand or by an electric motor. A rod attached to a piston within a cylinder lifts to suck water and waste from the bowl into the cylinder and expels the contents of the cylinder (flush water) above the piston into the bowl.

Manual duel action marine toilet illustration

Duel-action marine toilet - downstroke: water in/waste out illustration

Duel-action marine toilet - upstroke: water out/waste in illustration
When you work the handle on a double-action piston pump, two things happen when the piston goes up, and two things happen when it goes down, hence the name.

As the piston descends, it sucks flush water (raw or fresh, depending on how it's plumbed) into the cylinder above it and expels the wastewater below it into your downstream plumbing. If you've got it set to pump dry, the downstroke doesn't suck in more flush water above the piston because you've turned a valve to block off the water. The piston usually has a rubber ring around it to avoid liquid and waste passing between it and the cylinder walls.

A flapper valve sits between the bottom of the cylinder and the passage to the bowl. It must open wide on the upstroke to let the piston suck in the waste from the bowl, and it must seal well to keep the waste from going back into the bowl on the downstroke. This valve has a weight on top to help it to close firmly. Failure here results in waste being pushed back into the bowl on the downstroke.

A second valve, on the downstream side of the piston, must open to allow the piston to push the waste into the plumbing, then close and seal tightly to keep wastewater, which is often standing in the plumbing above the head, from seeping back into the bottom of the cylinder and, eventually, into the bowl. Often called a joker valve (or duckbill valve), its lips face away from the pump. Water pressure in the downstream plumbing helps by pushing the lips together. Failure here results in smelly wastewater coming back into the pump, and eventually into the bowl. A third valve lets air in when you want to pump dry, or it lets water in when you want to flush. Usually you operate it with a lever or a rotating handle. Its housing must provide an opening for the air to enter when appropriate, but it must not let water be pushed out of that opening when you're pumping. This is accomplished by several means, including small joker valves, which face inward from atmosphere, and other seal types, often involving O-rings, which wear over time. Failure here usually means water leaking out the air inlet hole.

Yet another valve must keep air from being sucked from the bowl into the cylinder on the downstroke (when you want to suck in flushwater and expel wastewater) and allow water to flow into the bowl during the upstroke. Often this valve is just a rubber ball held in place by a spring, and it operates automatically and is fairly reliable. A failure here most likely introduces air from the top of the bowl into the top of the cylinder, meaning that less flushwater will be drawn in. Any of these valves can become damaged or brittle with age or from chemicals or obstructed by debris, resulting in the problems mentioned above. As complex as this sounds, the operation of the double-action piston pump is really quite simple, and if you understand it, you'll diagnose and repair problems relatively easily.

Macerating Head

In a macerating head, an electric motor runs blades that not only push out the bowl contents but also chop up the contents in the process. An impellor may also be involved, which gives these heads the ability to push contents up as well as out — an important advantage in many plumbing runs. Most macerating heads also have one or more valves, such as a joker valve, to keep dirty water from backflowing into the head.

Macerating toilet illustration

Macerating toilet pump parts illustrationA macerating head has a set of blades that spin when it pumps the bowl out, processing the waste on its way to the holding tank.

The operation is fairly simple, but typically, a total or partial flush failure occurs when the blades get clogged; you must then get inside the housing to clear the problem. Different manufacturers deal with this in different ways. Some offer a removable cover to clear the blades. With this method, it's important to have an easily removable cover plate and also good access to that plate. Sometimes the plates themselves cause problems because of such issues as seals. Interestingly, Raritan designed its Elegance and Atlantes lines of heads without a cover plate. If one of these clogs, depower the unit and use a 45-degree, long-nosed pliers or similar tool and reach in from the bottom of the bowl to pull out the offending "foreign material." Your macerator head should have instructions in the manual for dealing with this type of problem.

Another typical failure is a burned-out motor, which must be replaced. A macerating head usually requires another pump to inject clean water from your boat's freshwater supply (which helps to avoid smells and calcium buildup) or from overboard. If this second pump fails, you don't get enough flushing water. A failure is usually caused by a fouled pre-filter screen (it's easy to clean) or bad valves in the pump, which can be replaced by removing the pump head. The Raritan Elegance and Atlantes lines of heads have a selector switch to allow you to use either water source by utilizing a solenoid valve.

If yours is an "automatic" head, a logic board operates the components as required, but a fault in the circuitry can halt this, and the board must then typically be replaced. If you must push a button to start the macerator and push levers to manually control the addition or removal of water, there's less to go wrong. On any head, anytime there's a lever, valve shaft, or piston rod with water inside the component, there's a shaft seal, which must be replaced occasionally. You'll know the time has come when water begins seeping around the seal. These leaks are usually slow, and placing a towel to soak up the water as it comes out may solve the problem until you get back.

Vacuum Heads

Push the button on a vacuum head, and it's all gone quickly, with a whoosh. It's great, but as usual, there's more to these devices than meets the eye. Vacuum heads operate with a vacuum pump and tank that can be located up to 50 feet from the bowl; so says Dometic's SeaLand, which makes the VacuFlush. If you operate a lever or push abutton, the bottom of the bowl (the flush ball) quickly swings open, and the existing vacuum sucks out the contents. The vacuum pump must maintain a vacuum in the vacuum tank by turning on when a sensor detects a loss of vacuum in the tank. If the vacuum pump doesn't come on, the sensor may be defective and will require replacement. SeaLand, like other manufacturers, offers repair kits that you should keep on board for many problems that may occur. Two joker valves are typically found at both ends of the vacuum pump (for a total of four valves), and these may need to be replaced or cleared if there's a clog that causes stoppage or damage to them. These valves help prevent the loss of vacuum in the pump/vacuum tank components. Be sure not to change the direction of any joker valve when you replace it. Valve failure usually means you don't get that lovely flush, and you're stuck with either what was initially in the bowl or backed-up smelly water.

Vacuum toilet illustration

Vacuum toilet parts detail illustrationA vacuum generator sucks the waste from the bowl and sends it toward the holding tank with a quick whoosh.

A well-seated seal must keep air and water from being slowly sucked below the bowl when the toilet is not used. Usually the seal is around the bowl's bottom or, with some brands, under the seat cover. If the vacuum pump keeps cycling on more than normal, the seal needs to be replaced; this usually isn't very hard to do. If you don't have a spare seal, cleaning the leaking seal with your fingers and rubbing some silicone grease or other recommended product over the seal may rejuvenate it for a while.

A VacuFlush type of head typically uses much less water than other styles of heads; it also often utilizes the boat's freshwater supply via a supply pump, thus sharing potential issues and fixes associated with macerator heads. Some macerating heads, such as Raritan's Elegance model, also use only small amounts of water, making it practical to use a boat's freshwater supply. In a head using the boat's water supply, expect to find a vacuum breaker. This keeps a column of air between the water going into the bowl and the boat's supply of potable water. A vacuum breaker may use a joker valve, a ball-and-spring assembly, or another method to open the line to atmosphere after the supply pump stops but to close it to atmosphere while the pump is running. Leaks at the vacuum break indicate a bad joker valve or other seal or O-ring. However, some heads, such as the Elegance, locate this vacuum break within the bowl so that leaks go there rather than onto the cabin sole. 

Tom Neale, a technical and lifestyle writer and liveaboard cruiser, leads our distinguished "Ask The Experts" team.

— Published: April/May 2015


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