Valve examples to choose from

Valves are an important component in aquarium filtration systems. They start, stop, and regulate the flow of water and prevent leaks in case of emergency or maintenance tasks. You’ll find valves used in refugiums, contactors, protein skimmers and on water pumps. Even canister filters use small shut-off valves on the quick-disconnect feature.

If you’re building or modifying a filtration system with valves, you’ll find a dizzying array to choose from online and in stores. However, not all valves are the same. Some valves are designed for regulating air flow or gases like propane. Using the wrong valve can reduce the flow rate and make it difficult to maintain your filtration system or even leach metal into your aquarium water. Here’s what you need to know about aquarium-safe valves and how to choose the right valve for your setup.


Let’s start off with the assumption that we’re discussing valves for controlling water flow in an aquarium. You can immediately eliminate the following types of valves from your shopping list. Most of these are found in big-box home stores.

  • Brass ball valves
  • Copper plumbing valves
  • Gas valves
  • Compressed air valves
  • Aquarium air pump valves
  • CO2 fine adjustment valves

There are a variety of reasons not to use these valves. Any metal can corrode in salt water and cause problems and gas valves are normally made of metal. Aquarium air line valves aren’t water-tight and often have metal parts. Some check valves have metal springs or hinges. Look for valves made of PVC. They’re completely safe and fully compatible with your PVC pipe and fittings. The two most-used valves in aquaculture, public aquariums, and hobbyist aquarium systems are ball, gate valves, and check valves. 


ball valve example

Ball valves have a spherical (ball) closure unit. The ball has a port (bore) through the center. When the valve handle is positioned so that the bore is in the same direction as the pipe, it’s in the open position, and water can flow through it. When the handle is rotated 90°, the ball turns and the bore becomes perpendicular to the flow path, closing the valve and stopping the flow. Ball valves come in a variety of sizes for almost any plumbing idea you can think of. They are typically used on the return water line to easily cut the flow of water but can also be used to regular flow to an extent.  

ball valve diagram of open and close positionsExample of ball valve positions from open to close

Types of Ball Valves - Ball valves come in a variety of sizes to match common PVC pipe sizes. The most basic and economical ball valve has slip fittings on both ends. The valve is glued onto the PVC pipe. Other options include the use of one or two true unions connections which make it easy to remove the valve for cleaning or temporarily remove hard piped equipment, like a return pump or reactor. Simply close the valve, loosen the union nut and the fitting can be removed.

Full Bore vs. Reduced Bore - A inside a reduced bore ball valve is one pipe size smaller than the valve's pipe size. This restriction causes a reduction in flow rate. The main purpose of a reduced bore ball valve is to throttle back the flow even when the valve is fully open. Full bore ball valves are more common in the aquarium hobby. The inside flow area of the valve matches the pipe size. If you’re shopping for a ball valve, just be aware of the difference and how it might affect your application. 


Gate valve example

Gate valves have a flat closure panel that moves up and down instead of a rotating ball. The gate is connected to the stem of the handwheel. When you turn the handwheel, the gate moves up, allowing water to flow. Rotating the handwheel counterclockwise, lowers the gate back in place, stopping the water flow. These are best for your drain where regulating flow is desirable.

You may come across something called a knife or dump valve. They’re in the gate valve category but are made for applications where you want a fully open or closed valve without turning a wheel or lever. Just pull or push the handle to open or close the valve. It’s like an on/off switch for water.


Check valves are designed to only allow water flow to go in one direction. The check valve is installed on the return line, between the return pump and return inlet. This prevents water from back siphoning when the aquarium return pump is shut off, which could otherwise cause a flood. When the pump is on, the water pressure pushes the valve open. When the pump is shut off, gravity will close the valve. Check valves are also used for auto-top-off plumbing, so that aquarium water does not back siphon into the RO or RO/DI reservoir.


Ball, gate, and check valves come in a variety of sizes and fitting configurations. While ball valves are the most popular style, gate valves are a bit more compact, in terms of the handle. The rotating handwheel fits in places where the lever on a ball valve may interfere with the filter system. Some aquarists like the precise flow control of a gate valve vs a ball valve. Where as check valves do not adjust the flow rate.

To choose the right valve note that PVC fittings are listed according to PVC pipe sizes, not the actual measurement of the part, and are categorized by the types of connections they make:

  • MPT, or male pipe thread, has threads on the outside wall
  • FPT, or female pipe thread, has threads on the inside wall
  • PVC slip fitting, or slip fit, has no threads and glues to PVC pipe
  • PVC insert fittings, or hose barb fittings, connect to aquarium tubing (not flex PVC pipe)


valve examples to choose from that are great for reactors

Two Little Fishies offers a one-piece ball valve with barbed fittings which makes it easy for attachment to flexible tubing.

You might also encounter "quick release" valves which are common on canister filters and smaller diameter flexible tubing where a union is not practical.  These simply make disconnect easy and allow you to stop the flow of water before disconnecting.  

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