Seal the Deal: Everything You Need to Know About Rubber O-Rings

Why should I change the rubber O-Rings in my pump?

There are many parts in your pumps that keep it running smoothly, things like the mechanical seal, the impeller, or the bearings. But one of the simplest but also most critical components in your pumps is the humble rubber O-ring. It plays a huge role in holding in all the pressure, letting the mechanical seal function and preventing leaks.

In this article, we will break down what O-rings are, how they work, where they’re used in pumps, how to install them properly. We will also cover why a tiny dab of silicone grease can save you both time and money in pump repairs.

What Is an O-Ring and Why Does It Matter?

An O-ring is a simple loop of rubber, usually circular in cross-section but sometimes with a flat or square surface, that fills and seals a gap between two parts. It might not look like much, but it’s the first line of defence against leaks in most types of water, fuel, and chemical pumps.

O-rings have 3 main functions:

1. Maintain pressure inside a pump system
2. Prevent external contaminants from entering
3. Reduce wear on metal and plastic parts by acting as a cushion

Where You'll Find O-Rings in Pumps:

• Between 2 halves of an outer pump casing.
• Inside the pump attached to the diffuser/impellor housing, to separate the suction and discharge sections of the pump mechanism.  
• In mechanical seal assemblies
• Around pipe fittings and suction lines
• In pressure switch, pressure gauge or priming ports

When the pump is running, O-rings get compressed between metal (or plastic) parts, creating a tight seal that stops fluid from escaping or air from entering. Without that seal, your pump can lose pressure, suck in air, or start leaking all over your shed floor.

How O-Rings Prevent Leaks

O-rings work by forming a compressive seal. When they are fitted into the gap between 2 parts and then the bolts or threads are tightened, this squeezes the O-ring material causing it to deform slightly.

This deforming causes the O-ring to fill in any small gaps or surface imperfections, which along with it being impervious to water helps form a wide, flexible, sticky surface which stops water passing though the gaps in the pump. The O-ring also has the benefit that when water pressure is applied to it, this extra force causes the surfaces that form the seal to be squeezed with more force so it actually seals better. 

According to a Pump industry magazine article, seal failure and leakage is the main causes of downtime in pump systems. As o-rings play such a critical role in the seal mechanisms on a pump, then its imoirtant they are checked and maintained.

Why You Need to Inspect and Replace O-Rings Regularly

Like tyres or gaskets, O-rings don’t last forever. They wear out, dry up, or get damaged during cleaning or reassembly. If you’re not checking them now and then, you’re risking a slow leak or even full pump failure.

Watch for these signs:

• Flattened cross-section (called "compression set")
• Cracks or visible splits
• Swelling or chemical damage
• Leaks around sealed areas

We recommend giving your O-rings a once-over every 1 to 2 years, or anytime you service your pump. Its also cheap insurance to replace the main O-rings in your pump when doing a service so you aren’t pulling it apart again in a few weeks to fix a leak that has formed.

How to Install a New O-Ring Properly

Installing an O-ring isn’t hard, but there are simple things that can be done wrong if you are not paying attention.

Here’s how to do it right:

1. Turn off and depressurize the system. Safety first.
2. Remove the old O-ring carefully — using things with sharp edges can damage the groove that the O-ring sits in or other seal faces.
3. Clean the groove thoroughly. Get rid of grit, dirt, or old grease.
4. Inspect the sealing surface for scratches or burrs.
5. Lubricate the new O-ring with silicone grease.
6. Install without stretching or twisting. Lay it flat in the groove and make sure it sits in place properly.
7. Carefully fit the components back together, making sure that the O-ring hasn’t fallen out of place or slipped and is getting pinched or twisted where it won’t form a proper seal.
8. Tighten pump components evenly — this ensures the O-ring isn’t crushed, or pushed out of shape.
9. Test the pump once finished to make sure there are no leaks or drips and everything works correctly again.

O-Ring Materials: What’s Best for Your Pump?

Not all O-rings are made equal. The type of rubber matters, especially if you're pumping something other than clean water.

Common O-Ring Materials:

These are the most common types of rubber materials used to make O-rings.

Nitrile (Buna-N)

• General purpose

• Great for water and some oil applications.
• Affordable and widely available

EPDM

• Excellent for hot water and steam
• Resistant to ozone and UV
• Not suitable for petroleum products

Viton (FKM)

• Handles harsh chemicals and high temperatures
• Used in chemical dosing pumps or irrigation with fertigation systems and solvents. Also very useful when pumping diesel or petrol which can soften Nitrile rubber.

Silicone

• Soft and flexible
• Great in extreme temps (hot or cold)
• Suitable for food grade applications.
• Not as abrasion-resistant — best in static applications

At Rural Pumps the majority of our stocked O-rings are Nitrile rubber, but we do have a couple of Viton options and in our mechanical seals we stock a lot of high wear seals with Silicone Carbide faces and Viton Rubber seals.

Why Silicone Grease Is a Must (And Why Vaseline Is Not)

If you want your new O-ring to seal properly and last longer, don’t skip the lube — but make sure it’s the right type. 

Benefits of Silicone Grease:

• Prevents rubber from sticking or tearing during install
• Helps the O-ring seat properly in the groove
• Reduces wear from friction
• Doesn’t react chemically with rubber
• Safe for use in drinking water systems (if food-grade)

Why Petroleum Jelly or WD-40 Is a Bad Idea:

• Can break down rubber over time
• Causes swelling, cracking, or softening
• Often reacts with EPDM and nitrile
• Not designed for long-term sealing — it dries out

When it comes to applying the grease to an O-ring, place a little on your finger (it isn't harmful) then pinch 3 fingers together and drag the o-ring between your fingers to coat the surface. You just need a shiny coating to make it work properly, too much can get really messy. 

This is one of the reasons why we sell our Silicone Grease in handy little tubs for your toolbox. Having some Silicone Grease on hand to smear a fine coating on any O-ring when its being installed, makes getting things back together easier and lets your seal last a lot longer too.

Final Tips for Pump Owners and Repairer

• Keep a spare O-ring kit for your specific pump — especially if you can’t afford to have the pump not working.
• Always use the correct size and material for your application.
• Use only silicone-based lubricants on rubber seals.
• Inspect O-rings during every service — it takes seconds.

O-rings might be cheap and simple, but they’re critical to the performance and lifespan of your pump. Take care of them, use the right grease, and you’ll avoid breakdowns, leaks, and the stress of trying to replace parts in the middle of summer.

Got a leaking pump or need spare seals? Contact Rural Pumps — we stock high-quality O-rings, mechanical seals and silicone grease that’ll keep your gear running smoothly.