# A Study on Liquid Leak Rates in Packing Seals
## 3 Experimental Testing  
Leak tests with a set of four packing rings were conducted on the universal packing rig shown in Figure 2a. The rig had different modules to test stuffing box packing seals. The equipment was capable of performing gas and liquid tests at room and high temperatures. The test rig had three tubing systems, including a hydraulic tensioner tubing system that allowed the load to be applied to the gland through the stem using a hydraulic tensioner and a hand oil pump. The load on the packing rings was measured by means of a Wheatstone strain gauge bridge bound to the outside surface of the stem. A gas pressurization tubing system supplied pressure to the packed stuffing box using an air operated electronic valve and regulator connected to a 2400 psi gas bottle. Finally, an instrumented leak detection system for gas or liquids was connected to the packing rig leak collecting chamber to measure leaks. The universal packing rig was equipped with instruments to monitor pressure, gland stress, temperature, time, and leak rates, using a data acquisition and control system connected to a PC running a LabView interface program.  
The packing test module shown in Figure 2b consisted of a housing, 104.8 mm (4.125 in.) in height, in which up to 7 packing rings of 9.5 mm (3/8 in.) could be inserted in square section. The axial displacement of the packing rings due to compression was measured by two Linear Variable Differential Transducers, LVDTs placed diametrically opposed. The rig was equipped with five different leak measurement systems (based on different techniques) to be used depending on the level of leak rate that needed to be measured. These were: flow meter, pressure decay, pressurized rise, and mass spectrometry, to cover a leak range from 10 to 10\({}^{-10}\) mL/s for gases. A liquid leak measurement device that could measure leaks ranging from 1 to 0.00001 mL/s was also included. In this study, only the flowmeter and the pressure rise methods were used to measure helium leak rates and characterize the porous structure. The test module shown in Figure 2b was specially designed to include a central hollow cylinder inserted inside the housing between the packing and the stem. This created a tight chamber, so that the packing rings could be installed in the stuffing box inside a bucket filled with the test liquid to keep air bubbles from getting trapped in the system. The packing dimensions were 57 mm (2.25 in.) in outside diameter and 38 mm (1.5 in.) in inside diameter. The stem was made of SA193 B7 material with a diameter of 28.6 mm (1.125 in.).  
Figure 2: Universal packing test rig: (**a**) gas test module and (**b**) liquid test module.  
The special liquid leak measuring device shown in Figure 3 was used successfully in [15]--and was used here to measure leaks down to 10\({}^{-5}\) mg/s of water. The outside leak collection chamber was also filled with the same liquid, allowing only a 2 mL volume of air to be compressed during leak measurements. Any leak into the collecting chamber compressed the small air volume and increased its pressure. The liquid leak measuring device was composed of a liquid supply and purge system to operate safely and protect the 2 psi pressure transducer.  
The gland stresses, ranging from 10.34 to 24.14 MPa, were applied to the set of packing rings through the hydraulic tensioner fixed to the stem. For every level of gland stress, helium gas or liquid pressures ranging from 0.34 to 2.76 MPa were applied in steps, and the leak rate was measured. Additionally, the experimental samples were braided flexible graphite packing and graphite die rings. All tubes of pressurization and the leak detection system were thermally isolated to avoid the influence of temperature variations on pressure and therefore on the leak measurements.