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Variable Spring Rate Quench Valve

IP.com Disclosure Number: IPCOM000199634D
Original Publication Date: 2010-Sep-23
Included in the Prior Art Database: 2010-Sep-23
Document File: 6 page(s) / 132K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

A mechanical valve is fitted to the primary vent path of the MRI (Magnetic Resonance Imaging) system, which is designed to open in the event of a quench. The standard method of holding the valve seat in the normally closed position is by applying a force from a spring. These springs maintain a constant spring rate so that the force required to open the valve remains the same throughout the pressure relief operation. The choice of spring value is very important and is based upon three main factors: 1. Ensuring that the valve opens so that the helium vessel pressure does not exceed the design pressure. 2. Ensuring that enough force is applied to keep the valve shut (and leak tight) during normal operation. 3. Achieving a maximum installation height for the system.

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Variable Spring Rate Quench Valve

Idea: Philip Alan Charles, GB-Oxford; Trevor Bryan Husband, GB-Oxford

A mechanical valve is fitted to the primary vent path of the MRI (Magnetic Resonance Imaging)

system, which is designed to open in the event of a quench. The standard method of holding the valve

seat in the normally closed position is by applying a force from a spring. These springs maintain a

constant spring rate so that the force required to open the valve remains the same throughout the

pressure relief operation. The choice of spring value is very important and is based upon three main

factors:
1. Ensuring that the valve opens so that the helium vessel pressure does not exceed the design

pressure.
2. Ensuring that enough force is applied to keep the valve shut (and leak tight) during normal

operation.
3. Achieving a maximum installation height for the system.

When choosing the spring rate value, these factors conflict with each other. A low spring force is

desirable to keep the pressure (during a quench) at a minimum, but a high spring force is required to

keep the valve leak tight, and achieve the altitude requirement.

The current design quench valve is dependant on atmospheric pressure. The total force (in the

opposite direction to the gas) is the sum of the force produced by the spring plus the force produced

by atmospheric pressure. This means that when the quench valve is tested at sea level, the force

required to open it is higher that if the magnet was installed at 3000m. When the magnet is installed at

3000m, the force required to open the valve is much lower due to the effect caused by the reduced

atmospheric pressure. This increases the risk of the valve leaking.

Thus, the force required to open the valve must be greater than the force of the spring plus the force

provided by atmospheric pressure. When the atmospheric pressure reduces due to increased altitude,

the force required to open the valve also reduces. If the desired outcome is that the valve always

opens at the same pressure, then when the altitude increases, then force provided by the spring must

also increase.

The novel solution provides a quench valve that is independent of altitude, and can be set on site

during installation for the correct atmospheric pressure. So the spring rate is provided by a number of

springs in bending. The force required to open the valve is proportional to the free length of the spring.

This design is based on one end of the spring clamping method being adjustable, thus changing the

free length of the spring. The valve is set at sea level, which is when the clamped distance of the

spring is longest. As the distance decreases, the spring rate increases.

When the magnet arrives on a site at an elevated altitude, the position of the spring clamps are moved

so that they are shorter, thus effectively increasing the spring force, which compensates for the

reduced atmospheric pressure. The net effect is that the valve opens at the sa...