Common water pump mechanical seal types and materials

What are the different types of mechanical seals that are used in pumps?

When it comes to your water pump, the mechanical seal is a critical component for making the pump operate correctly. They’re designed to stop pressure leaking at the point where the pump shaft meets the housing. Without the seal, your pump would not produce pressure and flow correctly and it would create a lot of mess from the water spraying everywhere. As there are a lot of different types of pump to perform different functions, there are also a lot of different types of mechanical seal. Let’s break down the common types of mechanical seals you’ll encounter in water pump systems and the standard sizes they come in. If you need a new mechanical seal for your pump we have a wide range IN STOCK in our webshop. 

The Main Types of Mechanical Seals

Generally mechanical seals used in water pumps are mounted internally, so that means the parts are fitted to the inside of the pump housing. This means that the pressure created by the pump is used to push against the seal and help seal the mechanism. Occasionally in special industrial and mining applications a seal is mounted externally, this is limited to situations where the material being pumped is very corrosive or abrasive and to minimise contact with the seal, it is fitted into the pump housing from the outside.

Seal function

For internal seals, there is generally 2 types of function:

1. Pusher Seals
   Pusher seals are the most common mechanical seals out there. They use a spring-loaded design where the rotary face of the seal has an O-ring seal against the shaft to hold pressure in. This mechanism is then pushed against the stationary section using a spring that is fitted between the back of the impellor and the rotary. The spring pressure slides the O-ring mechanism down the shaft and keeps it tight against the stationary and this adjusts as the seal face wears down over time. These seals are versatile and work well in a variety of applications, from household water pumps to industrial systems. Their cheap cost, flexibility and durability make them a go-to choice. Their drawback is they generally have a limit of approx. 10 Bar (1000kpa) so they’re not always ideal for high-pressure or high-temperature environments.
2. Non-Pusher Seals
   Non pusher seals, work by sealing the rotary against the shaft away from the seal face and this mechanism does not move. There is then a rubber or flexible metal bellows which connects this part to the actual rotating seal face. As there is an air gap between the shaft and the bellows, then the shaft being smooth and the fluid being pumped can be dirty and there is less risk of o-ring damage and premature failure. These are great for handling extreme pressures or fluids that might damage more traditional designs. If you’re dealing with hot water or chemicals, non-pusher seals might be what you need.

Cartridge Seals

For certain applications, primarily where the pump internals are difficult to pull apart or too difficult to disconnect from its operating position, then the way to install your seal is to have it as a cartridge seal. A cartridge seal has both the rotary and stationary sections built into one mechanism. This mechanism is slid down the pump shaft from the outside and is generally screwed into a tread in the pump housing. An O-ring seals the rotating section against the shaft and it is fixed in place with a grub screw. The 2 most common applications for cartridge seals is in vertical multistage pumps. These high pressure pumps are very common in commercial irrigation and industry. As they can have 10 or more impellors, there is a lot of moving parts and can be complicated to pull apart. The other main application is in heavy industry for slurry pumps, these super heavy duty single impellor pumps are designed to pump heavy mud slurry in mining and processing. As they are very heavy and difficult to pull out and rebuild and the seals wear out regularly, then cartridge seals are used to make it fast and easy to carry out maintenance. They do have a slightly higher cost than a standard seal but the convenience they offer is worth it. We stock a range of cartridge seals for both Davey, Southern Cross and Grundfos vertical multistage pumps HERE in our webshop. 

Picking the Right Seal for the Job

Choosing the right type and size of mechanical seal depends on your pump and its operating conditions. Consider factors like:

• The pressure and temperature of the water.
• The type of fluid being pumped (clean water vs. abrasive or chemical-laden liquids).
• The size and speed of your pump motor.

By matching the seal type to your pump’s specific needs, you’ll extend its lifespan and avoid unnecessary downtime. For the size of the seal, you are restricted to fitting a seal that fits the dimensions inside the pump housing.  The main dimensions that are critical are:

• The depth and internal diameter of the pump housing back plate where the stationary fits. This determines the thickness and diameter of the stationary.
• The pump shaft diameter and distance from the back of the impellor to the stationary face. This determines the size and length of the rotary section. The clearances of the shaft and impellor to the pump housing also have to be checked.

Most of the time with replacing a seal, you simply measure the old seal and get an exact same size and type then you shouldn’t have a problem. It is a good practice to just check the manufactures parts listing as sometimes an incorrect seal has been used to repair the pump previously so confirming you have the right one is a good idea.

Material Matters: How Seal Materials Influence Performance

Not all mechanical seals are created equal, and a big part of what sets them apart is the materials they’re made from. The type of material used in a seal plays a massive role in how well it performs—and for how long—in different water pump applications. Let’s take a closer look at the most common materials you’ll find in mechanical seals and why they’re chosen for specific jobs.

Seal Face Materials

1. Carbon Graphite
   • Why It’s Used: Carbon graphite is a go-to material because it’s self-lubricating, lightweight, and has low friction. It works great in clean water applications and is often paired with harder materials like ceramic or tungsten carbide for durability.
   • Where You’ll See It: Household water pumps, irrigation systems, or any low-pressure, low-temperature setup.
   • Watch Out For: Abrasive fluids (like sandy water) can wear it down quickly. Salt water applications like seawater or pool pumps can also wear this quickly as salt crystals form in the seal surface and then rapidly wear the graphite out.
2. Ceramic
   • Why It’s Used: Ceramic is tough and resistant to corrosion. It’s an excellent option for systems handling clean water and moderate temperatures.
   • Where You’ll See It: Domestic water pumps and light-duty commercial systems.
   • Watch Out For: Extreme temperatures or highly abrasive conditions can crack or degrade ceramic seals over time.
3. Silicon Carbide
   • Why It’s Used: This material is ultra-durable, highly resistant to abrasion, and can handle extreme temperatures and pressures.
   • Where You’ll See It: Heavy-duty industrial pumps or pumps that deal with abrasive slurries, chemicals, or hot fluids.
   • Watch Out For: It is a lot more expensive, so it’s often reserved for high-performance or specialized applications.
4. Tungsten Carbide
   • Why It’s Used: Tungsten carbide is a powerhouse material—it’s hard, resistant to wear, and can handle high-pressure systems better than most other options.
   • Where You’ll See It: High-pressure water pumps, oil and gas systems, or other industrial applications.
   • Watch Out For: Its high cost makes it overkill for simple, low-pressure systems and clean water.

We have a range of SILICONE CARBIDE   and CARBON CERAMIC seals available in our webshop. 

Elastomers (Rubber O-rings)

1. Nitrile Rubber (Buna-N)
   • Why It’s Used: Affordable, flexible, and great for general-purpose water applications.
   • Where You’ll See It: Standard water pumps that handle clean or slightly dirty water.
   • Watch Out For: Not suitable for high temperatures or exposure to chemicals.

2. EPDM
   • Why It’s Used: Excellent resistance to heat, ozone, and some chemicals.
   • Where You’ll See It: Pumps handling hot water or systems exposed to outdoor environments.
   • Watch Out For: Avoid contact with oils or hydrocarbons—they’ll degrade EPDM quickly.
3. Viton (FKM)
   • Why It’s Used: Known for its resistance to chemicals, heat, and oils, Viton is a premium choice for more demanding applications.
   • Where You’ll See It: Pumps dealing with chemical-laden fluids or high-temperature systems.
   • Watch Out For: It’s pricier than other elastomers, so it’s not necessary for basic water systems.

Spring and Metal Components

1. Stainless Steel
   • Why It’s Used: Corrosion resistance and strength make stainless steel the most common for springs and structural components in mechanical seals.
   • Where You’ll See It: Pretty much everywhere, from household pumps to industrial setups.
   • Watch Out For: Prolonged exposure to certain chemicals or salty environments can cause pitting or corrosion.
2. Hastelloy
   • Why It’s Used: For the most aggressive chemical applications, Hastelloy is a corrosion-resistant alloy that stands up to the harshest environments.
   • Where You’ll See It: Pumps in chemical plants or wastewater treatment facilities.
   • Watch Out For: It’s expensive and overkill for everyday water pumps.

Matching Materials to Applications

The key to picking the right mechanical seal isn’t just about durability—it’s about compatibility with the pump’s operating conditions. This is the most common selections for various applications:

• Clean water systems: Carbon graphite and ceramic seals with nitrile rubber rings.
• Hot water systems: Silicon carbide faces and EPDM elastomers.
• Chemical-heavy systems: Tungsten carbide faces and Viton rings.
• Abrasive fluids: Silicon carbide all the way, with stainless steel components for extra toughness.

When you choose the right materials for your mechanical seal, you’re not just extending its lifespan—you’re protecting the pump, avoiding downtime, and saving yourself a ton of headaches.