What are Pressure Gauges?
What is a Pressure Gauge?
A pressure gauge is a device used to measure the pressure of a gas or liquid within a piece of equipment they are connected to. They are usually found in a range of equipment including pipework, filters, pressure vessels, and Pumps. 
When a pressure gauge is connected to the inlet of a pump and the discharge of a pump the difference between the two figures is what the pump is producing. Pumps produce a differential pressure within a system meaning whatever pressure is received at the inlet, the pump will produce its design pressure and flow in addition meaning the outlet pressure will be equal to the Inlet pressure, plus the pressure produced by the pump.
Gauges are essential when commissioning a pump to enable various checks to be made. These include confirming that the pump is producing its design pressure, to help balance the system by ensuring the pump is operating on curve and finally to confirm that the pump has sufficient suction pressure (NPSHA) to work in accordance with its design. Sometimes pipe work feeding pumps can feed other equipment, it can be untraceable often travelling through floors, behind walls and outside making it difficult to understand if there is an underlying issue with the system, and address it.
Pressure Gauges on the discharge of a pump are of a type which displays pressures in set ranges, for example between 1-10 bar, or 1-15 bar. Gauges on the suction part of the pump are typically a compound gauge meaning they read both positive and negative pressures. The glass part is filled with Glycerine as the pressure can fluctuate. The Glycerine helps to provide a more reliable reading, lubricates working parts, and has a stable viscosity across a range of temperatures helping to improve accuracy. Units on a gauge are usually Bar, M, or PSI.
Where are Gauges Connected to on a pump and what does a pressure gauge assembly consist of?
A set of pressure gauges are connected on a pump as follows. The Discharge pressure gauge is connected to a ¼” port at N1 on the below drawing. A compound gauge is connected to N2. Port N3 is used for filling the casing or venting air, N4 is used as a drain casing plug for emptying the pump head and N5 is used to determine if there has been a shaft seal failure.
N1 - Discharge Pressure Gauge Port
N2 - Suction Pressure Gauge Port
N3 – Priming Plug for filling casing or venting air
N4 – Drain Casing Plug
N5 –Seal Leakage Drain Plug
The correct installation schematic for pressure gauges is below. Firstly, isolating valves are connected to the pump suction and discharge ports. A siphon is then connected which enables more stable pressure readings to be obtained, as the reading should be fairly stable. Siphons can be U Shaped, Pig tail or O, or cylindrical shaped. A second isolating valve is then added to enable the siphon to be vented and flushed periodically. Without gauges it is not possible to accurately determine what pressure the pump is producing. 
4 Benefits of Pressure Gauges:
1. Speed up commissioning as it is possible to tell very quickly if a pump is operating as per its design pressure.
2. Provides clear direction of whether there is a system or pump issue
3. Assist with balancing pump ensuring pump does not cavitate leading to premature failure or frequent spare parts replacement.
4. Provides instant reference point for ensuring frequent monitoring. If gauges are only used during commissioning and then removed it can be difficult to pinpoint which equipment requires maintenance.
