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How a Regulator Works

Pressure regulators are ubiquitous in modern fluid system designs. They allow a system to contain fluid at a much higher pressure (and density, for compressible pneumatic fluids) than the main component’s operating pressures, which ultimately leads to higher energy density in storable fluid systems. Just how does a regulator accomplish this? Read on to find out.

A pressure regulator is a rather simple example of a mechanical closed loop feedback system. By sensing, or ‘reading,’ the pressure at its outlet, the components of the regulator will automatically adjust the position of the poppet to control the flow of fluid through the valve. This is commonly accomplished through the use of surfaces on the poppet which enact a force on the poppet, which is balanced by a spring or controlled pressure volume. When the outlet pressure of the valve produces a force which is equal to the balancing or reference force, the poppet contacts the seat of the valve and the regulator reaches a stage known as ‘lockup.’ Since the poppet’s seating surface is in contact with the valve seat, no fluid can flow through the valve. The outlet of the valve will then remain at constant pressure until the other components of the fluid system cause a change in pressure downstream.


As the pressure drops downstream of the regulator, the force on the poppet holding it closed will relax, and the poppet will be forced down by the reference. Fluid is allowed across the seat area, and the flow occurs until such time that the system builds up enough pressure downstream to close the regulator again. This is referred to as the flow state of the regulator.

Due to this simple design, an ideal regulator with no friction or pressure would produce a constant downstream pressure at both flow and lockup conditions. This would significantly ease the burden on the design of the downstream components, since the pressure range they would have to be able to work under would be small.

As with all practical systems, the poppet of a pressure regulator does not move instantaneously from open to close when the downstream conditions change. This time differential results in more fluid flowing across the seat area than necessary. The end result of this mechanical inefficiency is a downstream pressure at lockup which is higher than intended.

This effect, known as overshoot, is a critical parameter of any regulator. Overshoot, along with the pressure drop which occurs as fluid flows freely through the valve, create a band of pressure conditions over which all downstream components must be capable of operating. For most space based missions, the sensitivity of downstream components to pressure changes is high and thus, minimizing their exposure to these off design conditions is of critical importance to regulator design.

To address these fallbacks of typical pressure regulators, Castor Engineering employs a number of techniques. Our regulators incorporate Direct Sensing Technology, where the downstream pressure is measured by the poppet almost immediately after the fluid passes over the valve seat. This configuration, along with very small sensing volumes, allows Castor regulators to achieve extremely fast response to downstream conditions, with minimal overshoot. Castor regulators also employ another method to ensure fast response: the diameter of the poppets in our regulators is significantly oversized in comparison with the line size of the valve. This allows for high flow through the valve with very little stroke, thereby minimizing the travel necessary to close the valve at lockup. Single stage Castor regulators consistently achieve less than 5% overshoot under normal operating conditions.

For applications where 5% overshoot is unacceptable, CEI also offers multiple stage pressure regulators. These are essentially multiple regulators connected in series with one another. The primary, or ‘knock-down,’ stage is used to bring the inlet pressure down to a very narrow band, which is then fed into the secondary stage. Since the secondary stage is not exposed to the full pressure variances of the inlet, it can be much more sensitive to inlet and outlet conditions, thus improving overall outlet conditions. Castor multiple stage regulators typically achieve well below 1% overshoot, with an equal decrease in the pressure difference between flow and lockup conditions.

As with all Castor Engineering products, our regulators are meticulously hand built and tested by our technicians at our La Habra, CA facility. Every piece of hardware delivered to our customers has gone through rigorous inspection and testing before it ever leaves the building. This is all part of our goal to bring to you the utmost in precision and quality for your fluid control needs.