Sealing Integrity of Plastic Valves: How Tight is Tight?
- Expertise
Sealing Integrity of Plastic Valves: How Tight is Tight?
“Oh, there's a drop.“
“A few drops are insignificant.“
When asking about the assessment of a valve's tightness, one receives quite divergent answers. While some tolerate no droplet formation within 24 hours, others indicate that the formation of drops at minute intervals is permissible.
In both cases, the valve is attested with the characteristic of “leak-tightness”.
Standards help ensure a consistent set of requirements for the property of "tightness." With regard to plastic valves standards that provide guidance on Valve test and determine a Valve tightness:
Test standard ISO 9393-2
Describes the procedure for plastic valves the leak tightness of plastic valves .
Product Standard
The product standard ÖNORM EN ISO 16138 specifies requirements for the design and tightness of diaphragm valves made from thermoplastic materials.
The test conditions and the requirements for the result are provided by test standard ISO 9393-2.
In detail, it applies that the plastic valve must be tested both for its external tightness and its tightness in flow. During the entire test duration, no visible leakage is permissible.
If no visible leakage can be detected during the test period, the clear requirement is met. The test is then considered passed.
The image provides a view of the sealing surface of a DN 50 diaphragm valve, showing unacceptable droplet formation according to ISO 9393-2 during the test duration.
This is carried out in the form of a cycle test. During this, the valve is under pressure, and the 20 °C medium flows through the valve, including the test setup. After 5,000 cycles, during which the valve is opened and closed, the plastic valve is finally tested and evaluated for its tightness.
The criteria are comparable to those of ISO 9393-2.
The leak rate indicates how much of a medium flows through a leak in a unit of time. The specification is usually given in mbar*l/sec.
In the field of metal valves, according to EN 12266-1, there is an alphabetical categorization of the leak rate. Starting with leak rate A up to leak rate G, the tightness of a valve is assigned to a category, whereby with each successive letter, the leak rate increases, meaning the valve exhibits a larger leak and thus greater leakage.
If we combine the standard requirements for plastic valves the unit of measurement "leak rate," the following evaluation criteria apply to the valves:
Leak-tightness Test: ISO 9393-2, EN 12266-1 (Leak Rate A)
If the plastic valve is tested according to the specified test conditions of ISO 9393-2, the plastic valve meets leak rate A.
Leak rate A corresponds to the definition in standard EN12266-1. The definition of leak rate A states that no visible leakage occurred during the test duration, thus reflecting the requirement of the test standard.
All Praher Plasticsplastic valves these quality standards.
Comprehensive tests in the development of a valve, and furthermore, a 100 percent control in the production process, ensure the highest degree of tightness.
