Water supply pressures from municipal sources can reach levels of 150 psi or more. This is well above the pressure limit of many components in a micro-irrigation system. Therefore, it is important to utilize a pressure-regulator in any micro-irrigation system, especially if the water is provided by an independent source. Keep in mind that supply pressures may vary considerably with demand, which in turn, can vary with seasons and time of the day. Therefore, measuring the source pressure is often not a good indication of what the pressure may be or could be.
Pressure regulators are available in a variety of configurations and sizes. Each has its own input pressure limit, output pressure limits and flow rate constraints. Some pressure regulators are available in which the output pressure is fixed, within certain flow limits, while in others the output pressure is adjustable.
Fixed output pressure regulators are primarily made of plastic and have input pressure limits of about 125 psi. These regulators are available at flow rates up to 32 gallons per minute and output pressures up to 60 psi. These regulators are available in several sizes and with a wide selection of output pressures ranging from about 10 psi to 60 psi. Some fixed output pressure regulators are available that are made of metal. These have input pressure limits of about 300 psi. However they usually have relatively low flow rates to compensate the high pressure.
Most pressure regulators are flow sensitive. If the flow rate exceeds the recommended limit, the output pressure can decrease significantly. For example, if a 50 psi fixed output pressure regulator rated at a maximum of 32 gpm is used with a system having a flow rate of 40 gpm, the output pressure may drop to about 40 to 45 psi. Transversely, if the flow rate does not meet the minimum flow required, the pressure regulator may not regulate at all and the down stream side of the system will see the same pressure as the up stream side. A micro irrigation system should always have a pressure regulator even with the use of pressure compensating emitters. Care should be taken in the selection of a pressure regulator, always double check your flow rates.