Modulate steam valve

metrosilo

I've been working with steam systems for about 5 years now. I recently had a conversation with a co worker about modulating the amount of steam going into a coil in a air make up unit. I was always of the understanding that a steam valve is either open all the way or closed. The minute you modulate, any steam hitting the partially open valve will immediately condense. Anyone have any insight into this topic? Or an article research about this.
Thx

mikeg2015

You can modulate steam on 2 pipe systems with a steam trap, it just one pipe that you cannot.

All industrial process and a most large commercial steam systems have modulating valves.

The valves are expensive.

mikeg2015

Here’s an actuator. You’d need a controller, sensor and properly sized valve. There are examples, you need to verify caompatability or any adaptors needed... ad flow rates/capacity.

https://www.supplyhouse.com/Belimo-WGVL-EVB24-MFT-Warren-Globe-Valve-Linkage-w-Non-Spring-Return-Modulating-Valve-Actuator-MFT-24-VAC-DC


https://www.supplyhouse.com/Siemens-599-03077-2-Way-1-Control-Valve-Steam-10-Cv

https://www.supplyhouse.com/Johnson-Controls-A350PS-1C-Proportional-Temperature-Control-30F-to-130F-0-10VDC-4-20MA


Just an example.

metrosilo

Thanks for reply. I guess I'm more curious as to why it can be done. With hot water systems, yes, I understand when you slow the flow, you can control temperature going into the coil. With steam, I was told that it's either on or off. No inbetween. So if you're saying yes, that means that when you slow the flow of steam, you can control the temperature going in and out?
Basically, gas versus liquid.

JUGHNE

If you slow the flow of steam, less of the coil will heat up.
The temp of the steam will be the same, just less steam to condense. Partially heating the coil.

If the hand valve you use for throttling is on a vertical pipe then some condensate could form above that riser.

Works only for 2 pipe systems, not 1 pipe, as the condensate has to flow back thru that valve as the steam comes in.

Jamie Hall

You are controlling the amount of steam going in to the unit, and hence the amount of heat which can be released -- which will control the temperature.

And yes, steam can be modulated -- even low pressure steam. With a few considerations. The first thing to remember is that when the steam goes through the valve, some of it will condense. If the valve is at the point of use, that isn't a problem -- you want the heat release there anyway. That's point one. Point two is closely related: you have to be able to do something with that condensate. Again, in a two pipe radiator or a steam coil etc., that's not a problem -- you already have an outlet (usually trapped -- not always; see all the stuff on orificed vapour systems!) so the condensate goes away. We'll get back to a one pipe system in a moment. If the modulating valve is on a steam main, you will need to have a drip just downstream of the valve, even if it is parallel flow. That must go to a wet return unless there is also a steam trap -- then it could be a dry return if the dry return is low enough. Now one pipe steam. The inlet valve must always be, as you have heard, either open or closed. The reason there is a little different: the condensate in the radiator or whatever has no other way to get out, and if the valve is partly closed, it has to fight with the steam trying to get in, which causes all kinds of usually noisy mischief

metrosilo

I should have mentioned that the modulating coil I'm talking about is on a two pipe system. Trap on the return.
In most of the buildings I worked on when I first got started we're one pipe systems. That's why I was always of the understanding that valves always have to be open or closed all the way.
Thanks for info guys! This is my first time on this site!

motoguy128

> @metrosilo said:
> Thanks for reply. I guess I'm more curious as to why it can be done. With hot water systems, yes, I understand when you slow the flow, you can control temperature going into the coil. With steam, I was told that it's either on or off. No inbetween. So if you're saying yes, that means that when you slow the flow of steam, you can control the temperature going in and out?
> Basically, gas versus liquid.

To Clarify, steam temperature depends on pressure. Just like a refrigeration system. You can only control the flow of the steam Which changes the amount of surface area that is heated.

2 pipe radiators can be modulated.
Many of the old steam radiator valves for 2 pipe radiators, have marks on them to regulate the flow.