Occasionally, you may have an application where a single Jordan Valve Sliding Gate regulator will not be able to handle the required pressure drop. Two regulators installed in series can handle the pressure drop with good sensitivity while avoiding the problems encountered when taking large pressure drops across one valve.
Let’s look at an example:
You need to regulate 500 psi down to 50 psi. Line size is ½” and the maximum flow rate is 250 scfm. The medium is air at ambient temperature. Your preference is to use a self-operated regulator instead of a control valve. As the maximum pressure drop for a 1/2” Mark 60 with Jorcote seats is 400 psi, one valve will not work as the delta P on the application is 450. One solution is to split the pressure drop by installing two valves piped in series, thereby providing a two-stage pressure drop.
The first step is to determine at what pressure you stop the first stage and start the second stage. The intermediate set pressure is adjusted to obtain the maximum output through both regulators.
Use the following formula:
P2 = √(P1*P3). P1 = 500 psi, P3 = 50 psi, then P2 = √(500 x 50) = 158 psi
The first valve can now be sized for 500 psi inlet (P1) to 158 psi outlet (P2). The second valve must be sized for 158 psi to 50 psi. In doing this, you will find the second valve requires a higher Cv than the first valve to handle the larger volume of lower pressure air. The first valve in the series will be a 1/2” Mark 60HP with a range of 75 – 190 psi and a 1.6 Cv. The second valve should be a 1/2” Mark 60 with a range of 20 – 55 psi and a 4.4 Cv with double dome bolting.
Important items to note:
Always use the equation (P2=√(P1*P3)) to determine P2. This assures the ratio of inlet pressure divided by outlet pressure for each valve is equal so the upstream valve does not overly influence the downstream valve.
The second valve in series must be capable of handling the maximum inlet pressure (500 psi) in the event the first valve fails; thus, the double dome bolting.
The second valve should be installed at least ten pipe diameters downstream of the first valve.
Keep this in mind the next time you have an application with a pressure drop that exceeds what one valve can handle.