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valve

Valve

Device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically valves fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

Types

Programmable valve

Nonprogrammable valve

Nonprogrammable valve.


An analysis of the evidence did not demonstrate a clear advantage for any specific shunt component, mechanism, or valve design over another.

In the nineties, more than 30 valves have been launched, most are “clones”, but some introduce new concepts (Diamond, SiphonGuard, PaediGAV). Of the 22 designs we tested, 20 have no previous tests and 3 are low-cost valves from Mexico (Dewimed), Zimbabwe (Harare-shunt) and England (Nottingham Shunt). 27 were tested using non-stop-perfusions for 365 days, 8 for 168-294 and 3 for 2 days.

Ranking of the mean relative deviation: adjustable valves 19%, gravitational 34%, simple ball 51%, diaphragm 73%, distal slit 74% and autoregulating valves 121%. Ranking of physiological flow properties: gravitational > Equiflow > autoregulating > adjustable > ball > diaphragm > distal slit.

The Equiflow were highly susceptible to external pressure.

Most valves designed in the nineties showed inaccuracy, long-term-drifts, safety deficits and hydraulic mismanagement similar to more than 400 previously tested probes. With regard to accuracy and drift the ball designs were superior, but simple and adjustable ball valves are at risk of overdrainage. The gravitational ball valves (Cordis GCA, Miethke valves) showed the closest relation to physiological flow requirements 1).

Integra valves

Medtronic valves

1)
Oikonomou J, Aschoff A, Hashemi B, Kunze S. New valves–new dangers? 22 valves (38 probes) designed in the 'nineties in ultralong-term tests (365 days)'. Eur J Pediatr Surg. 1999 Dec;9 Suppl 1:23-6. PubMed PMID: 10661786.
valve.txt · Last modified: 2019/04/18 13:00 by administrador