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Lou Okonski on Non return valves sticking

By: Lou Okonski [1187] 1 Stars
Date: Wednesday, January 19, 2011
Time: 8:08:43 AM

Than you much for the attention to my post. The 6 right angle non return sits on the top of the steam outlet which sits on top of the steam drum of a 20,000#/hr CE boiler. The steam will leave the boiler vertically and turn 90 degree through the valve. Down stream there is a gate isolation valve. The line then travels from the isolation valve into the main steam header for distribution. This setup is identical on the four boilers. Importantly, the non return protects personel and property by closing in the event of a tube failure or the like and not allowing steam to discharge through the plant. As many of you know, a non return is a code requirement in a multi boiler system going into a common header.

Another function the non return supplies is to bring the boiler on line by allowing the disc in the valve to slide open when the valve disc sees enough force to lift. The pressure differential needed to lift the disc is calculated by the weight of the disc and the surface area of the disc with a little friction small amount thrown in. This I understand is 1/2 psi to 2psi or therabouts. There may be a little chatter as the valve seat lifts.

When buying an NRV, it becomes important to size the NRV to the steam flow of the boiler not necessarily to the outlet size. In most plants that we are in the NRV is sized to match the outlet. That means that many NRVs in the world are oversized. Obviously the outlet has been designed to allow for maximum steam that the boiler can supply or more. What this says to me is that we cannot simply look at the valve and replace in kind. It also beggers a question Has something changed and what?. When replacing a NRV with a smaller one, a code spool piece would have to be made on both sides of the valve. This complicates matters in a retrofit because of the dimensional change. Oh that we could just change like for like. This is an area of the steam plant that is overlooked.

Again, has something changed such as the design of the NRVs or is this something that valve manufacturers are doing due diligence on after years of just selling. I have heard from the people that both sell and rebuild valves that there is a difference between older valves and the newer imports. I myself have more confidense in an old rebuilt because of being bit hard in this situation. With four valves from the same manufacturer, bought at the same time, slamming at 30-40 psi differential something is wrong.

The leak by on old valves most likely comes from a worn seat. The seat wear can be from erossion or seat chatter. These are easily machined and often at 1/4-1/3rd the cost of a newer valve 6 and up. We have gotten numerous valves rebuilt with success. There were a few that were too far gone.

Mostly, I wanted to share my experience with the message that NRVs are not as simple as may first be seen. Also wanted to get feedback from this respected forum.
Thank you

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High Sulfite Residual
By: Ross. [390]

First, I want to say that large amounts of Sodium Sulfite NaSO3 becomes a contaminate because it will produce foaming and other problems, but foaming is the primary problem.

Your 500-psi Water Tube Boiler is seems to have reasonable level of residual Sodium Sulfite NaSO3 remaining in the boiler water. Nice pH too.

Your 300-psi Waste Heat Recovery Boiler has twice what I would expect for Sodium Sulfite NaSO3 at ranging 80-ppm to 100-ppm. pH is good so you are getting a good yield.

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