"non-slam" check valves
"non-slam" check valves
(OP)
Dear All,
I just want to know what is the action of a non-slam swing check valve. My understanding is that it is non-slam in one direction (i.e. when the disc slams against the body during opening) and that the non-slam action arises due to the opening of the disc in a direction of compression of the spring.
During closing action, however, the spring assists, in addition to gravity and reverse pressure force, and the closure of the valve is quicker.
Various mfrs implement this "non-slam" action by different designs. Some call it "cushion" check valves too.
I am looking forward to comments from members here on the purported action of this "non-slam" or "cushioning" device, as I am trying to sort out some confusions over the matter with my colleagues.
Regards
I just want to know what is the action of a non-slam swing check valve. My understanding is that it is non-slam in one direction (i.e. when the disc slams against the body during opening) and that the non-slam action arises due to the opening of the disc in a direction of compression of the spring.
During closing action, however, the spring assists, in addition to gravity and reverse pressure force, and the closure of the valve is quicker.
Various mfrs implement this "non-slam" action by different designs. Some call it "cushion" check valves too.
I am looking forward to comments from members here on the purported action of this "non-slam" or "cushioning" device, as I am trying to sort out some confusions over the matter with my colleagues.
Regards





RE: "non-slam" check valves
RE: "non-slam" check valves
1) In our industry we have the non slam check valves by Eagle Industry Co Ltd. They call it "Free Flow Reverse current valve with Oil Cylinder"! In principle it is a normal swing check valve and the hinge pin extends beyond the body to connect to a spring loaded piston which travels in a cylinder. The bottom portion of cylnder is connected to Oil supply header (~5kg/cm2g) and the upper portion to oil return header . When the disc swings open, the action is to compress the spring and the pressured oil (@5 kg/cm2g) fills up the displaced volume.
This action, in my opinion, effects a non-slam action against the body.
Upon disc closure, the spring force (with its stored potential energy) quickly swings into action and aids in quick closure. The, trick now is that the spring closes quickly but is moving against a pressured header which offers resistance. So in effect the valve closure upto 80-90% (just a guessed number, depends on spring constant) is very quick but the rest of the travel is slow. Thus this kind of check valve perhaps effects non-slam action in either directions. Before i did this post, my understanding was that of "non slam action only in one direction, i.e. while opening".
2) I saw the air-cushioned and oil cushiooned swing check valves offered by APCO valves. The operation of their valve is well explained in their catalogue.
Essentially both use the piston and cyliner. And in addition they have a "COUNTERWEIGHT" arm; this counter weight arm can be adjusted to give varying load arm (moment).
2.1) In the air cushioned design, the disc opening action draws in air (freely) in to the cylinder through a (yet another) small check valve - which is actually a "control check valve". There is no spring to be compressed here, so the disc travel is free (and this is clearly highlighted in the APCO catalogue) and must "slam" the valve body.
In the pressure reversal case, the disc closes quickly under the influence of the counter-weight; the fastness of closure being adjustable (depending on the load-arm selected). the quick closure takes the valve to about (say) 80% during which time the piston is compressing air within the cylinder . After this 80% closure, the pressurised air in the cylinder acts as a cushion and the full closure is ensured under the controlled release of air from this control check valve.
The APCO catalog states that the user can alter the closure time by altering the load-arm; and alter the cushioning effect by playing with the control knob on the "control check valve" of the cylinder.
2.2) the oil operated case is similar to the air cushioned swing check valve as explained above. APCO states that, sometimes during rapid flow reversal, the "air cushiooning" may lose its effectiveness; and in such cases they recommend the oil controlled check valves.
I would like to thank you again for your post; it just made me look at the other side of the coin too. Please correct me if i have lapses in my understanding . Thanks
PS: Just for your information, we are using the swing check valves as explained in 1) above in Gas and steam services.
Regards
RE: "non-slam" check valves
RE: "non-slam" check valves
You may not be aware of a non-slam nozzle type check valve.
It combines all advantages of the other check valve styles.
1. non-slam performance without any dampening system. it has very small valve disk strokes, that gives small reverse velocities, when the disk hits the seat. (Imagine clapping your hands with a distance of 1 inch and 10 inch and you know the difference)
2. Low pressure loss due to venturi-shaped design leading to big energy cost savings.
3. Maintenance-free design due to metal-to-metal sealing without wearing parts to be replaced regulary for several years of operation.
If you need further info please look at www.noreva.de
RE: "non-slam" check valves
They might be able to assist you.
RE: "non-slam" check valves
Another one is from Stockham, the "noz-check"