Two types of Vacuum Control
There is a lot of confusion about vacuum regulators and how they work.
There two major types of vacuum control devices: vacuum regulators and vacuum breakers. This page seeks to explain the different purposes of each type, and how they work.
Vacuum Breakers (Vacuum Relief Valves)
Most regulators used to control vacuum let ambient air into the vacuum system to control the vacuum pressure. This type of regulator is often called a Vacuum Breaker or Vacuum Relief Valve. On this website, we will use the term Vacuum Breaker. These regulators are actually a type of Pressure Reducing Regulator because the pressure controlled is at the outlet port. The regulator opens to increase absolute process pressure (or reduce vacuum level).
Vacuum breakers typically use a spring loaded diaphragm with atmospheric pressure on the upper side and process vacuum pressure on the lower side. In this simplified example at right, the spring actually pulls the diaphragm up to provide the negative set-point pressure. When the absolute process pressure becomes too low (vacuum too high), the plunger forces the valve seat down, allowing more outside air into the process. As the absolute process pressure increases, (vacuum pressure increases) towards set-point, the plunger rises again to restrict the in-flow of air.
The other type of regulator works by throttling flow between the vacuum pump and the process in order to control the proccess vacuum. This type, which will be referred to as a Vacuum Regulator, is actually a Back Pressure Regulator because the pressure controlled is on the inlet port. The regulator closes to increase absolute system pressure (or reduce vacuum level).
In the simplified example at right, the process vacuum is also on the lower side of the diaphragm, and the atmospheric pressure on the top. The spring is also pulling up to provide the negative set-point bias. But the action of the seat is reversed. As the process pressure becomes too low (vacuum too intense), the plunger again lowers, but this results in a further restricting of the gas flow. As the absolute pressure increases above set-point (vacuum too low), the plunger rises and the gas flow from the process to the pump is increased.
Some vacuum regulators are considered “relieving vacuum regulators”, which mean that they can allow gas into the process when the set-point of the vacuum regulator is reduced (to increase absolute pressure). Others are considered “non-relieving vacuum regulators”, which means that gas flow must be provided from another source in order to lower the vacuum intensity in the process. Fortunately, most vacuum process have at least a small amount of in-leakage, alleviate the concern when using the non-relieving type. Some vacuum regulators provide relief by allowing a small but controlled amount of in-leakage into the inlet port.
Larger vacuum regulators are often referred to as Vacuum Control Valves. Equilibar sells vacuum control valves as large as 6″ in size.
Pros and Cons of Vacuum Control
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Precision Vacuum Control
Unfortunately, most vacuum regulators and vacuum breakers suffer from significant pressure variations when gas flow rates change. It is relatively easy for a regulator to hold a set process pressure while the vacuum supply pressure and flow rate remain steady.
But as either one of the process conditions change, most spring adjusted vacuum regulators and breakers suffer from significant droop and drift.
A few manufacturers, including Equilibar, utilize a 2-stage regulation process to obtain more stable results than is achievable with a single spring-loaded stage.
For more details, see how the Equilibar 2-stage Vacuum Regulator works.
Is the Equilibar Precision Vacuum Regulator right for your process?
A simple vacuum breaker may be sufficient for your process if you do not require precise control, or if your vacuum pump requires a minimum gas flow rate. Read more about our high precision vacuum regulators, or contact our engineers to discuss your application further.