Quantcast

Leaky Check Valve

Help Support HMEM:

blockmanjohn

Well-Known Member
Joined
Apr 24, 2016
Messages
128
Reaction score
6
Hi,

I built a small check valve as part of a Jan Ridders designed engine. The valve seat was cut with a small boring bar at 45 degrees. It then uses a 3/16" steel ball to make the seal. There is no spring pressure on the ball. In any event, the valve leaks. I noticed that there are tiny, concentric grooves on the seat which were left by the boring bar. I think that if I were to some how polish the seat all would be well.

My plan is to turn an aluminum rod with a 45 degree chamfer to size, chuck the seat in the lathe, charge the rod with 1200 grit compound, use low speed and gently feed the rod into the seat with very little pressure until the seat is smooth. Does this sound like it would work? Is there a better way to do this? The valve is made from brass.

Thanks in advance, John.
 

cheepo45

Member
Joined
Dec 22, 2010
Messages
241
Reaction score
74
I built a Jan Ridders Debbie 2 stroke. All you need to do is put the check ball in and using a small punch, tap it with a hammer to seat it. It worked great for me. It's best to use a new ball after seating it.
If you need any more info on this engine, feel free to ask. I have sorted out a lot of issues with mine-now it runs great.
 

blockmanjohn

Well-Known Member
Joined
Apr 24, 2016
Messages
128
Reaction score
6
Thanks for the tip Cheepo. I'll give it a try. This is for Jan's Scuderi Cycle engine. I have it completed but can not get it to run yet. I'm hoping this will do the trick.
 

Charles Lamont

Well-Known Member
Joined
Mar 24, 2011
Messages
683
Reaction score
189
Location
UK, West Midlands
Many will argue that a check valve ball should sit on an edge, not in a cone. I think you would do better to cut the seat square. Using a slot drill or end mill will leave it slightly high towards the centre, which is even better. Then you pop a ball in, and do what cheepo45 said. If the through hole is roughly 0.7 times the ball diameter, the ball will sit on the seat with a 45° tangent.
 

stackerjack

Well-Known Member
Joined
Sep 12, 2014
Messages
51
Reaction score
7
I'm sure you guys know more about check-valves than me, but consider this:-
By tapping the ball with a hammer, you are increasing the area of contact of the ball. This means that for a given force, from the spring, there will be less PRESSURE between the ball and the seat.
Jack
 

deverett

deverett
HMEM Supporter
Joined
Sep 6, 2007
Messages
1,165
Reaction score
234
Location
Skibbereen, West Cork
Instead of tapping the ball, another way is to glue a ball to a rod that has been centre drilled and twiddle the ball back and forward on the seat to burnish it. Just a few twiddles usually does the job. The rod should fit the top part of the valve to keep everything normal.
Obviously a new ball will be required for the valve afterwards.

Dave
The Emerald Isle
 

Kerrin Galvin

Active Member
Joined
Jan 10, 2012
Messages
32
Reaction score
9
The other idea is to use a silicon nitride ball, instead of giving it a belt put it in Valve & both in the vice using a rod against the ball & give it squeeze to form the seat. How much squeeze is up to you... A couple of advantages of using the nitride ball is they are better dimensionally round & far harder, after using it for the seat you can use it in the valve. A stainless ball you need to throw away as it’s likely you will deform it.
Hope that’s is useful

Cheers Kerrin
 

cds4byu

Active Member
Joined
Apr 28, 2014
Messages
43
Reaction score
9
I'm sure you guys know more about check-valves than me, but consider this:-
By tapping the ball with a hammer, you are increasing the area of contact of the ball. This means that for a given force, from the spring, there will be less PRESSURE between the ball and the seat.
Jack
The pressure between the ball and the seat isn't the most important thing.

The most important thing is that there must be 100% contact between the ball and the seat. A knife-edge contact is nice because it's less likely to have bumps that prevent complete seating. But a burnished high-area seat will seal better than a lumpy low-area seat.

The relevant pressure for opening the valve is the force of the spring (or gravity, if there is no spring) divided by the area of the ball exposed to the fluid.

Carl
 

stackerjack

Well-Known Member
Joined
Sep 12, 2014
Messages
51
Reaction score
7
Carl,
You're probably right about the pressure, but I wouldn't like to even begin calculating the area of the ball exposed to the fluid.
Any ideas please?
Jack
 

Cogsy

Well-Known Member
Staff member
Global Moderator
Joined
Jul 30, 2012
Messages
2,887
Reaction score
851
Location
Perth, Western Australia
Carl,
You're probably right about the pressure, but I wouldn't like to even begin calculating the area of the ball exposed to the fluid.
Any ideas please?
Jack
Calculating the area of a sphere is simple math (4*Pi*radius^2) then you just need to estimate the proportion of the sphere exposed to the fluid itself. Alternatively, I would think it'd be approximately close enough to just use the area of the inlet pipe and treat the sphere as flat (area of a circle = Pi*radius^2).
 

tornitore45

Well-Known Member
HMEM Lifetime Supporter
Joined
Jan 17, 2009
Messages
953
Reaction score
187
Alternatively, I would think it'd be approximately close enough to just use the area of the inlet pipe and treat the sphere as flat (area of a circle = Pi*radius^2).
Not "close enough". Using the Flat projection of the sphere portion obstructing the inlet pipe is the EXACT area to use.

Any area that is not perpendicular to the pipe axis is symmetrically located around the axis and any radial force is balanced out.
 

Cogsy

Well-Known Member
Staff member
Global Moderator
Joined
Jul 30, 2012
Messages
2,887
Reaction score
851
Location
Perth, Western Australia
Not "close enough". Using the Flat projection of the sphere portion obstructing the inlet pipe is the EXACT area to use.

Any area that is not perpendicular to the pipe axis is symmetrically located around the axis and any radial force is balanced out.
I think for it to be exact we would need to integrate over the entire curved surface but at the scale we're discussing it's overkill.
 

cds4byu

Active Member
Joined
Apr 28, 2014
Messages
43
Reaction score
9
The area exposed to the fluid is A=pi(rx)^2

rx is the smaller of the pipe diameter and the (ball diameter)*sin(theta)/2, where theta is the angle between the centerline of the valve and the conical ball seat.

If one wishes to integrate over the entire ball surface, one can do so. But one must only integrate the component of the pressure parallel to the spring force; the component perpendicular to the spring force doesn't lift the ball.

The result of this integration is the flat projection of the sphere, as Mauro has said.

Carl
Provo, UT
USA
 
Last edited:

Ed T

Well-Known Member
Joined
Aug 7, 2009
Messages
179
Reaction score
2
In my previous life, we made tens of thousands of round balls in conical seats by coining (tapping) the ball into the seat. It was, most often, a carbide ball into a conical brass seat, but an ordinary ball bearing ball will work as well if it's harder than the seat material. One big advantage of this arrangement is that the ball will always seal regardless of the angle (within reason) of the stem it's attached to. A cone in a cone type of valve can be very sensitive to angularly off-axis articulation since, once off axis, the contact area wants to be an ellipse and it isn't, so it will leak.
 

Richard Hed

Well-Known Member
Joined
Nov 23, 2018
Messages
443
Reaction score
107
Location
Seattle
I'm sure you guys know more about check-valves than me, but consider this:-
By tapping the ball with a hammer, you are increasing the area of contact of the ball. This means that for a given force, from the spring, there will be less PRESSURE between the ball and the seat.
Jack
Now wait up, this seems obscure to me. Do you mean less pressure per unit area of contact between the ball and seat? Or something else?
 

fcheslop

Well-Known Member
Joined
Apr 7, 2010
Messages
867
Reaction score
237
Location
The land of the Prince Bishops
Just use a nitrile ball saves all the hassle
First use a steel ball of the same size give it a biff with a guided punch or just let a centre drill kiss the edge. The through hole is better reamed not drilled
Ideally the seat is coned upwards so that in use any dirt falls away from the seat
Iv never had a problem with Nitrile but had a s-it load of tears using stainless
 

Cogsy

Well-Known Member
Staff member
Global Moderator
Joined
Jul 30, 2012
Messages
2,887
Reaction score
851
Location
Perth, Western Australia
Now wait up, this seems obscure to me. Do you mean less pressure per unit area of contact between the ball and seat? Or something else?
Pressure is force divided by area so if you increase the area of the seat you are reducing pressure on the seat. It's why someone stepping on your hand with a stiletto heel hurts more than when someone wearing sneakers steps on your hand (I really need to spend less time sprawled on the floor at parties).
 

Cogsy

Well-Known Member
Staff member
Global Moderator
Joined
Jul 30, 2012
Messages
2,887
Reaction score
851
Location
Perth, Western Australia
The area exposed to the fluid is A=pi(rx)^2

rx is the smaller of the pipe diameter and the (ball diameter)*sin(theta)/2, where theta is the angle between the centerline of the valve and the conical ball seat.

If one wishes to integrate over the entire ball surface, one can do so. But one must only integrate the component of the pressure parallel to the spring force; the component perpendicular to the spring force doesn't lift the ball.

The result of this integration is the flat projection of the sphere, as Mauro has said.

Carl
Provo, UT
USA
Have you got a reference or at least a name for the equations you're drawing these from so I can look them up? I'm stuck on hydro-static pressure where we certainly need to integrate over the surface given the change in head pressure with depth. It's going to be minuscule in something this size, which is why I suggested we could neglect it, but my intuition says your equations are not truly exact. I would like to read up on it some more though - I haven't had much experience in fluid dynamics.
 

Richard Hed

Well-Known Member
Joined
Nov 23, 2018
Messages
443
Reaction score
107
Location
Seattle
Pressure is force divided by area so if you increase the area of the seat you are reducing pressure on the seat. It's why someone stepping on your hand with a stiletto heel hurts more than when someone wearing sneakers steps on your hand (I really need to spend less time sprawled on the floor at parties).
yES, Of course. What I am asking, is that the little ring of contact between the ball and seat gets smaller the cleaner everything is, (that is, the cuts) which would increase the pressure per unit area of contact--BECAUSE the total pressure in the check valve has stayed the same, just the area of contact has reduced (or increased) thus the pressure PER unit area goes up or down inversely. So the original post was very unclear.
 

Latest posts

Top