HH175 regulator

[R. Nelson]

I have a question concerning the regulator on my HH175. I have noticed that when I crank up my unit, I purge and sometimes the reg has changed from 20cfh 30-35cfh,...is this due to temp. variance, bad reg....any thoughts? It is not a major problem because I always check cfh output on startup, just want to know if there is a problem with my reg.

[Al T.]

Does it actually increase flow or is it just a sticking indicator?

[Hobart Expert Dave]

Sounds like a problem with the regulator. I have not seen this happen on any of the ones I have been using and I have used them in cool and hot weather. I would get it checked out.
Thanks
Dave Evans

[R. Nelson]

Originally posted by Al T.
Does it actually increase flow or is it just a sticking indicator?

It appears the flow actually increases it does not always do it, it is a random occurrance, example, last friday I hooked up new bottle of c25, set flow, welded for a while, closed bottle, purged, same on Tues. afternoon, Weds. afternoon, opened valve on bottle,purged and cfh was around 32cfh?

Any thoughts.

[jgor]

Rock,

Are you saying that when you close the bottle and then purge the flow gauge shows 30+ and then drops down to zero?

I just received my HH175 earlier this week and I noticed that when I shutdown and purge the flow gauge jumps from 20 up to about 30 and then slowly drops to zero. On mine it jumps up pretty quickly so if you're not watching the guage when you press the trigger you might miss it.

When I saw it happen I just assumed it was caused by the lack of pressure on the high side of the regulator. Unfortunately I have no idea if this is why it really happens or not but maybe the experts will know.

John

[Roger]

Simple question so here is a long answer.

You are using what's called a flow gage regulator. They have LP pressure gage callabrated to indicate flow through a known size orifice (small hole) by measuring pressure upstream of the orifice. When flow stops pressure will build up a little on all regulators that will indicate increased flow with no flow. If you have a ball in tapered tube flow meter it would indicate actual flow at zero flow.
Old pressure gages do tend to stick and go nonlinier. Old regulators with lots of use tend to have more pressure rise as flow stops and then free flows. Your flow gage will indicate a real high flow increase when flow stops if you have it set at lowest indicated flow on your gage.

Just thought what you are probably seeing. Most regulators are unbalanced. That means as input pressure lowers regulated pressure rises typicaly .5 psi for each 100 psi input pressure drop. So if your bottle pressure is 2000 psi and you close bottle valve then purge regulator inlet pressure you will see a regulated pressure rise or a flow increase on your flow gage with no flow. I don't know what regulated pressure would indicate a given flow rate but it would change if orifice size was changed or gas was changed.

If you ever need to replace your flow indicating gage the replacement must be calibrated for the same orifice size. Lots of different orifice sizes are used by different companies. Orifice is part of outlet fitting so you can change that with gage if you had trouble getting correct gage.

With a flow gage you can only set flow rate when gas is flowing and inlet pressure is stable and outlet pressure is stable. The flow gage has to have pressure down stream of orifice less than 5 psi to be accurate.

Hope this makes sence.