Mechanical seals are unsung heroes of the pumps in your HVAC plantroom. Their role is to keep the system truly closed-loop, preventing leakages from going out, and contaminants from going in. 

As with most components, you have a choice when it comes to spec. When it comes to mechanical seals, that choice is between ‘unbalanced’ and ‘balanced’ seals – though this terminology is slightly misleading, as we will discuss further in the article. 

Depending on your system’s needs – and the water pressure in your system – balanced and unbalanced mechanical seals can both save you money. 

It’s the classic dilemma of an inexpensive option that you’re hoping won’t break, battling it out against the expensive option that makes you question whether it’s something you actually need, or overkill. 

As both of these options are completely viable in the right context, this article will inform you on which choice is right for you, as it really is a matter to be handled in a case by case fashion. First, let’s understand what it means for a mechanical seal to be balanced: 

What is the ‘balance’ of a seal? 

Hydraulic balance refers to the distribution of load placed across a seal’s opening and closing areas. The closing area of the pressure on the outer diameter of the seal is different to the pressure on the inner diameter. 

Seals are therefore hydraulically balanced to control opening and closing forces on a seal ring, ensuring they are not severely unequal and prone to being displaced. Balance ratio measures the difference between Ac (closing area) and Ao (opening area). 

Therefore, the lower the balance ratio, the more balanced the seal. 

‘Unbalanced’ Seals 

The reason we say that the ‘balanced’ and ‘unbalanced’ terminologies can be misleading, is that all mechanical seals are technically hydraulically balanced to some extent. An ‘unbalanced’ seal is defined by having a balance ratio of more than 1, and typically sits at approximately 1.2. 

They are limited to dealing with a pressure of 16 bar or less, making them unsuitable for high pressure pumps. However, if your system’s maximum pressure falls underneath 16 bar, there is no advantage to upgrading from unbalanced seals, making them the more economical choice. 

Balanced Seals 

Conversely, a balanced seal is characterised by a balance ratio of less than 1. Most balanced seals have a balance ratio of between 0.65 and 0.85. 

Thanks to their tighter tolerances and more stable balance of Ao to Ac, balanced seals are the way to go for systems that use high pressure pumps that operate at 10 barg or more at their maximum operation.

Avoiding disaster

While unbalanced seals used on low pressure pumps will save you from the unnecessary premium of balanced seals for your individual application, using balanced seals on high pressure pumps will save you a whole lot more than the premium of using balanced seals. 

This is because with the use of unbalanced seals on high pressure pumps, you are risking leaks, the hazards associated with leaks, and dreaded system downtime. It pays to have a solid system whose every spec is governed by economical reliability. 

The Smart Choice

While using balanced seals for high pressure pumps is a requirement for reliable use, and fitting unbalanced seals can be problematic, using unbalanced seals for low pressure pumps does not make any concessions, and using balanced seals on them could be viewed as an unnecessary additional expense. 

As usual, it pays to know what you need and what you’re looking for. If you’re still not sure which option is right for you, or you’re looking to obtain the best value seals on the market,  get in touch with Masterflow and we will make sure you’re looked after. 

Our technical experts care about your success and are determined to connect you to the most effective solutions in accordance with your project goals.