The hosts knew that the early momentum would prove vital given the weather and by half-time they had established a 10-0 lead.
No 8 Sam Whittingham forced his way over for the try, with fly-half Greg Wood converting and then adding a penalty.
Tynedale had to play catch-up and, in trying to force the play, mistakes littered their performance.
Sandal were able to control the pace and when the moment arrived they made sure of the points.
Debutant prop Freddie Potrykus was on hand to get the ball over the line, leaving Wood to convert and snuff out the opposition’s remaining spirit.
Sandal are now fourth with 42 points from 14 games and are 17 points adrift of leaders Macclesfield.
Huddersfield saw their relegation struggle deepened by a 32-6 defeat at the hands of Preston Grasshoppers.
The two sides went into the game separated by just four points, with Huddersfield needing a win to revive their campaign.
However, in torrential rain and standing water, they were forced to call time on the game 10 minutes early, with Hoppers having already effectively secured maximum points.
After falling behind to an early try, Huddersfield hit back with two penalties from fly-half Chris Bell but that was as good as it got.
By half-time, the hosts were 15-6 behind and then 32-6 adrift by the hour, leaving both captains to shake hands on an early finish.
The result leaves Huddersfield at the bottom on 18 points, one behind Broadstreet, four adrift of Luctonians and five behind Tynedale.
Mid-table Otley suffered their third successive defeat, going down 27-19 at previous bottom club Luctonians.
The visitors had lost their last two while, in contrast and despite sitting at the foot of the table, Luctonians had won their last two.
The home side made the better start and went on to dominate the first half by taking a 20-5 lead, Otley’s try coming from second-row Jonathan Stannard.
However, a comeback after the break began with a penalty-try, converted by captain Stephen Depledge, to reduce the arrears to eight points.
A third try followed when centre Mike Coady crossed and Depledge again converted to leave the game on tenterhooks at 20-19.
Just when it seemed Otley may have rescued their situation, they conceded a try with 10 minutes remaining and Luctonians were in no mood to let victory slip from their grasp.