After the system is purged of air and with makeup water functioning, the circulating pump suction side pressure will be 12 – 18 psi, the discharge side of the pump will vary and is dependent on the pump curve and how it was spec’d. When the system is overcharged with water, suction side pressure will be higher 20–30 pounds as well as the discharge side. This does not mean more water is flowing and is detrimental to cooling as it generates heat.