Danfoss stop valve problems.

[Gurt Fengler]

G'day all,
just wondering if anyone else has had this problem. We recently had to upgrade a liquid make-up solenoid v/v and associated v/v's and pipework for an accumulator. As the job was on a branch line that supplied other operational accumulators, the decision was taken to renew the branch line stop v/v prior to the job to provide a safe "known quantity" lockout, as this branch line was to be offline for a few days, and the original valve had a questionable seat. We used a Danfoss DN50 straight stop valve with a 100mm handle.

This was shut quite tightly by hand (by myself, no valve key, no tool), locked out with a chain and padlock, and the job commenced, taking about 1 1/2 days. No smells, no problems. However, on the third day, while checking the uncommissioned line at the start of shift, to my surprise, I found it to be full of liquid NH3. When the new valve was checked it was found to be almost to the point of loose. The liquid line and the branch line were pumped down, the valve bonnet removed and the seat inspected - all ok.

The valve was reassembled and locked out the same way, checked again about 5 hrs later, only to find it quite loose again. This time I took the handle off and put a shifter on, turning approx 1/8 turn more. This seemed ok, however I am concerned damage to the seat may occur.

This new type had a black (neoprene?) seat compared to the older white (neoprene?) seats. I have noticed this problem on a lot of these danfoss v/v's, however not to this extent. There are no torque ratings in the directions for closing the valve, only for backseating.

Can't beat the old white metal seats huh?

Concerned.

[RANGER1]

Gurt,
Pretty common problem with Danfoss from my experience.
The seats are square when new, so needs to be seated a few times as it moulds to the seat (45 deg angle).
If we install one & the line is made live & are not connecting that day while we are there, we weld on a end cap with 1/4" purge valve installed.
The bigger the valve the harder to seal also.
I hate these valves, but not much else to choose from.
As you say whitemetal seat was always good or the latter weld in Valco also.

[Gurt Fengler]

Thanks Ranger1, I will have to monitor these quite carefully during our pumpdowns from now on.

[kiwi]

Are these the new SVL/SVA valves? Danfoss used to be the benchmark, now they are so hit and miss. I quite like the newer Hansen valves (when not recalled :p). The MVP platform valves are very useful. Yet to use the Danfoss option. The white metal valves certainly were great (until some arse swings on them with a 4' bar). Are Valco still around? Has Gordon Bros picked them up?

[mbc]

have you checked direction of valve.

[Tycho]

I've never had that problem with the smaller size danfoss valves, which way was the pressure on the seat?
Not sure if I remember correctly, but I think the valves are rated for a delta pressure of 15 bar if the pressure is in the flow direction of the valve, and I've had a few times when pressure testing parts of a system that the valves started leaking internally and I could give it another 1/4 turn to reseat it when the pressure was in the flow direction. Never had it when the pressure has been against the flow direction (as the pressure would push the seal harder against the seat).
On Larger valves (Dn150 and up) though I have had it just about every time I pressure test, especially the ones that have the loose shaft with nozzles through the seal to equalize the pressure when opening the valve, those I would have to tighten again and again, often with the help of a length of pipe to get it to seal, not optimal, but it gets the job done.

[RANGER1]

Are these the new SVL/SVA valves? Danfoss used to be the benchmark, now they are so hit and miss. I quite like the newer Hansen valves (when not recalled :p). The MVP platform valves are very useful. Yet to use the Danfoss option. The white metal valves certainly were great (until some arse swings on them with a 4' bar). Are Valco still around? Has Gordon Bros picked them up?

Valco stop valves have not been around for years, cannot compete against China unfortunately.
I think they make the sight glass valves & reliefs though.

[kiwi]

Valco stop valves have not been around for years, cannot compete against China unfortunately.
I think they make the sight glass valves & reliefs though.
I thought as much. I recently saw a new Mycom screw package with Valco relief valves and Gordon Bros test tags on them which sparked my curiosity. It was an irregular package for what we would see from Mayekawa so I guessed its an Aussie build?

[RANGER1]

I thought as much. I recently saw a new Mycom screw package with Valco relief valves and Gordon Bros test tags on them which sparked my curiosity. It was an irregular package for what we would see from Mayekawa so I guessed its an Aussie build?

Has it got a vertical oil separator on the end?

[kiwi]

Has it got a vertical oil separator on the end?No. Horizontal.

[Magoo]

Hi Kiwi
possibly a local weldtrade variant, next door to mycom office NZ.

[kiwi]

Hi Kiwi
possibly a local weldtrade variant, next door to mycom office NZ.
Took a look today and it is a Weldtrade assembly. Bit different with the oil pump in a difficult to service location under the oil separator and a loading assembly of four solenoids rather than a directional valve. Will have to hit Martin up about that.

[Gurt Fengler]

Kiwi, these are SVA valves.
mbc and Tycho,yes valve direction is correct.
The liquid line (1050kpa) this was branched off feeds some low pressure accumulators (-30kpa). These accumulators are fed by PM 1-25's used as solenoid v/v's. Even though liquid into accumulator is regulated back, when these PM v/v's shut, they still provide a kick/jolt to the high pressure line. This coupled with what RANGER1 suggested (square new seat) may provide an answer. Thank you all for your input, much appreciated.