How to

1 November 2016

Pressure Relief Valves/Vents (PRVs) in Walk-In Freezers


Pressure Relief Valves, also known as Pressure Relief Vents (although in either case abbreviated to ‘PRV’) are an integral component of an effective, efficient, easy-to-use cooling unit. They facilitate pressure equalisation (which, among other things, ensures that external doors can be operated easily), as well as helping the units maintain a constant, cool temperature, which thereby prevents any damage or spoiling of the contents of the unit, through either warming to room temperature, or the consequent build-up of ice crystals when melted liquid water returns to thermostat-prescribed temperature. The following guide explains PRVs, considering how they work, why they are important, and how you can easily work alongside and maintain them.

Pressure relief valves are a reliable means of maintaining a constant, controlled environment inside a cold storage unit. They have two predominant functions: pressure equalisation and the consequent retention of the desired air temperature.


Pressure Equalisation

Walk-in cold storage units almost always have cooling mechanisms which work by drawing warm air out of the room. One result of this is the desired drop in temperature; but a side effect is a somewhat less convenient change in air pressure – namely, a drop of air pressure inside the room. A difference in pressure on either side of a door, walls and roof can have various negative ramifications which the PRV counteracts.

  • For one, such a pressure difference can cause structural fatigue to the wall, roof, floor and door panels, causing them to need maintenance or replacement on a more regular basis than would otherwise be the case. 
  • Furthermore, a pressure imbalance can make it very difficult to open the door and access the walk-in unit itself. A common way around this can often be to get the strongest worker in the team to come and open the door for you – which is far from an ideal situation, not least because it reduces the efficiency of work. It could also put strain on team dynamics or even cause injury to those trying to open unusually heavy doors (or, indeed, to those constantly called upon by team members to open them).  
A Pressure Relief Valve is therefore capable of preventing such pressure imbalances, thereby preserving the unit itself as well as the working efficiency, team dynamics and overall safety of employees.


Retention of the Desired Air Temperature

When the door to the cold storage area is opened, warm air inevitably makes its way in. If the room is used to keep certain foods fresh, the hazards in such a case are obvious. Moreover, one might bear in mind that if ice is allowed to melt and then re-freeze, it can move, flow and accumulate in undesired areas, causing a maelstrom of problems – which range from needing to defrost the unit, to real structural damage if it the water seeps into the wrong places (think of how pot holes form when rain water seeps into cracks in the road and then expands upon freezing). Although the job of the cooling unit is to negate the effects of this, it sometimes cannot do so fast enough. This is where a PRV comes in handy, allowing warm air to escape from cold areas in a somewhat roundabout manner which is related to air pressure balancing. Essentially, if the PRV was absent, low pressure would be present inside the cold room. If there were simply a hole in the wall, air from the outside would be sucked into the room due to this pressure imbalance. But by negating this pressure imbalance, the PRV not only prevents this one-way air flow, but also allows warm air to flow out of the room, further facilitating cooling.


Working With and Maintaining PRVs

Keeping a Pressure Relief Valve in good working order is relatively easy. Preventative maintenance is by far the best way to achieve long-lasting results.


In the above image, you may note that the path to the PRV is clear: there are no obstructions which could prevent a good passage of airflow to the valves. Moreover, it’s good practice to check for clogs (such as dust or other small airborne particles) which might, over time, accumulate and stop the PRV working properly. Annual lubrication of moving parts is also advisable. The overall goal is to remove any obstructions to good, clean air flow. 

Pressure relief valves are absolutely essential to the effective running of walk-in refrigeration or freezing rooms. Being aware of what they are, how they work and how to keep them properly maintained is vital knowledge to anybody working with such equipment.


James Stannard

James has a Bachelor’s degree in History and wrote his dissertation on beef and protest. His heroes list ranges from Adele to Noam Chomsky: inspirations he’ll be invoking next year when he begins a Master’s degree in London.