# O-Ring Design for low pressure applications

I'm trying to figure out how to create a seal for a very low pressure gravity feed system. Essentially its a low pressure solenoid valve. Is there any equations to estimate the amount of force you would need on a o-ring to seal it from any leaks of pressure $$p$$ its placed in a spring solenoid combination so I need to have this as low pressure as possible. Any ideas on what force I would need from the spring to seal a liquid the pressure is due to a height of about 40mm with a liquid like water. So if my math is right that's $$\rho g h = 997 kg/m^3 * 0.04m * 9.81m/s^2 = 391.22\ pascals$$ at the o-ring so pretty small amount of pressure.

Also what material would you suggest for the O-ring I have considered, I have used 50 Durometer with no success and am thinking about moving to a silicone based O-Ring. I can't increase the force of the spring because a solenoid will need to overcome it and i'm limited on space.

• If you don’t create enough force between o-ring and solenoid it will leak... if the o-ring is a tight fit around the solenoid then control the fit of the o-ring in the bore. It will add to the load for the solenoid - is this a valve of some type - what about a collapsible pipe section being crushed as the pressures are low... – Solar Mike Sep 7 '19 at 3:28
• O-ring manufacturer's websites have lots of great information on how to design with O-rings. For instance applerubber.com. You can also call them and they are very likely to help you with your application. – Eric S Mar 1 at 0:09

Take a look at how irrigation valves work. In a nutshell, the solenoid blocks a small orifice with a cone shaped plug, or the shaft blocks an orifice. When the solenoid operates, the "leak" is used as pressure to operate the valve. Start here: https://en.wikipedia.org/wiki/Solenoid_valve

Another possible source of inspiration would be the valve system on natural gas appliances. Here, it's critical to not have leaks. Pressures are on the order of what you mention here.

Because you are using small forces, you may be able to get a better seal with an o-ring mounted in a groove on a shaft, and then use a long tapered bore. This allows the o-ring to wedge between the cylinder and the bore wall. The price you pay is needing a longer solenoid stroke to provide sufficient clearance for the fluid to pass.

Buna-N is a typical o-ring material and will seal at low pressure, standard is 70A. Make sure you lubricate them before installation, or they can tear and won't seal anything.

Apple Rubber or Parker Hanifin both have extensive o-ring application handbooks that will size everything for you.